Not that I really think that, obviously. In fact, one imagines (or at least hopes) no-one does. There is though, a significant amount of opposition to the idea. Several people have voiced their objections in person, and I spent some time this afternoon reading various other complaints scattered around the intertubes. All of them can be roughly divided into three camps.
1. This is a waste of money that would be better spent elsewhere.
Whether or not one considers this a waste of money is obviously down to personal preference. To my mind, it obviously isn't; putting together a campaign to reassure those that feel brow-beaten by religion (whether or not they actually have been) doesn't seem that bad an idea. Especially since it isn't really all that much money in the grand scheme of things. It's worth noting (as Andrew Brown did) that the Sidmouth donkey sanctuary raised two hundred times as much money last year. Now, I'm not suggesting keeping atheists happy is worth at least 0.5% of the money spent keeping donkeys happy, but it does suggest that any attempt to portray this campaign as leeching away money from other potential good causes is fairly foolish.
Besides all that, though, there's a more general point here, which is the "that money could have been better spent on X" is actually a fairly shitty argument when applied to large sums of money which have been generated by thousands of small voluntary donations (it's more convincing when discussing where our tax money goes, since we don't get to volunteer that). If, say Bill Gates were to suddenly say "I'm gonna spend $300 000 dollars on public transport that decries God", then it would be legitimate to ask whether he couldn't think of anything better to spend his money on. Demanding that the money raised for the Atheist Bus Campaign should be spent on a better cause (starving children and aid to war-zones being the two most common requests) completely misses the point that the money exists in the first place because people wanted to donate to that particular cause. If every person in the country buys one DVD for a tenner a year (which is massively low-balling it), then the total expenditure is over half a billion pounds. Think how much the Red Cross could buy for that. Does it bother these same people that all that money is going to waste on Mamma Mia - The Movie?
The "all that money spent on Y should go to X" can be applied to almost anything. If you want to say that not enough people give to charity, and not enough of those that do give sufficiently, then that's potentially a reasonable point (though you'd need some fairly compelling statistics before I wouldn't think you were just full of it). Acting outraged because the combined expenditure of thousands of people on something you think a waste adds up to a lot of money is just stoopid.
2. The message is too "in your face"; it's the Shouty Atheists having a go again.
If the first argument is misguided but understandable to a point, this second one is total bullshit on toast. There are two reasons why claiming the advertisement is too aggressive is idiotic. The first is comparative. The reason this campaign was launched in the first place was a direct answer to an earlier set of bus adverts that read "When the son of man comes, will he find faith on the earth?". There was also a web link on there, which took you to a website that left the reader in no doubt that their options were either accepting Jesus, or spending eternity burning in a lake of fire. Obviously not everyone who saw the message was likely to check out the link (which means those claiming that "this is just push-back for that advert telling people they were going to Hell!" are being somewhat economical with the truth), but even the text itself is somewhat unsettling. I don't think I'm reading too much into the quote to say it looks a lot like the "What will your father say when he gets home?" formulation familiar from my childhood. It isn't explicitly a threat, but it cannot be taken in any other way apart from the most random of questions.
Compared with that, the atheist message "There's probably no God. Now go out and enjoy your life" is very positive . It's the carrot, rather than the stick (this isn't the time to go into my problems with the idea of Hell, but I will say that I am continually baffled by those Christians who think the best way to persuade others that the infinite love and mercy of God is best sold to others by telling them "Believe in him, or else"). Had atheism attempted to respond in kind, the message would have been "There's no God; you're wasting your life if you think otherwise".
Of course, "They started it" isn't usually a particularly compelling argument. It is hardly possible, though, to consider a way that the slogan could be less aggressive. Adding "We believe" to the start is the only thing I can think of. Of course, that would only really be necessary if people automatically assume that anything written on the side of the number ten bus must be unquestionably true. And if that was true, then the quote given above (Luke 18:8, apparently) would have to have been presented as ""When the son of man comes, will he find faith on the earth? Assuming he hasn't just been made up, that is." One wonders if those protesting over the wording of the atheist slogan would insist on this change as well. What about other faiths? If a Muslim group wants to put "The One True God doesn't want you out every Friday night binge-drinking until you vomit into your kebab," do they have to add "That is, as far as we're concerned. It's all a bit hard to verify, y'know?"
Beyond all that, we'd have to adapt this theory to all advertising. "Stella Artois: reassuringly expensive. Well, that's what we think, but we work for them, so we're biased." It's a standard that isn't applied anywhere else. I don't think it should be applied, either, since I already despair of how carefully one has to avoid idiots taking you too literally (remember the "fictionalisation" label that cell-phone advert had to bear, just in case someone though you really could skip the damn thing across the entire Pacific Ocean). But if the atheists have to qualify themselves, then so does every bugger else.
The final thing to consider is the target audiece. The original Christian advertisement was aimed at non-believers. The threat is aimed at those who don't yet accept Jesus. This is anecdotal, but I've heard of a number of Christians complaining that these advertisements are an attack on their religion (I personally have only spoken to one). This is obvious rubbish to anyone who knows the history of the campaign, but I'm pretty sure this can be worked out without that knowledge. It's a simple matter of understanding the other side. Faith is an extraordinarily powerful thing. It can and has survived bereavement, war, crippling illness, and even the Holocaust. It would be ludicrous to imagine it could be broken by something so minor as a slogan on a vehicle. Given that, which is the more likely? That the people behind this campaign are targetting Christians, and are either are too stupid to know they're wasting their time, or know it but just want to bite their thumbs at the church anyway? Or that they're targetting other atheists, or agnostics, or those still unsure about whether they still believe in the Christian God or not? Attempting to colour this campaign as attacking Christianity requires an assumption that atheists are either stupid or mendacious (or both), which says more about the commentator than it does about the subject.
I said the Christian attempt at persuasion-through-public-transport was aimed at non-believers, but that might not be quite the right way to put it. Sometimes it's helpful to consider the relationship between Christianity and Atheism is to imagine as political rather than religious. There are the devoutly religious who cannot be dissuaded by atheistic arguments. There are atheists who are sufficiently secure in their (lack of) beliefs that no amount of Bible quotes and pictures of pitchfork-wielding demons will bring them into the flock. These are the base of each group. But there are also those who are unsure, the swing-voters, those who either have a history with a church that they haven't quite broken away from, or who are looking for spiritual meaning in a world that doesn't seem to provide it . Much like political advertising isn't designed to sway the faithful, but hoover up those in the middle, both of these campaigns seem to be aimed at those who have yet to make up their minds (or become content with) their religious outlook. The only difference is in the method of persuasion used.
3. "There is probably no God" violates advertising standards.
This third argument officially arrived on Thursday when Christian Voice complained to the ASA that the "advert" was "misleading" (h/t to Garathon for the link). This is by far the most interesting of the three arguments. There are two questions to be considered at this point:
- Should all (or even any) of the rule that apply to advertising products hold when advertising religions and/or philosophies?
- Assuming they should, is "probably no God" a sufficiently defensible statement?
 Though I did run into one person who thought that the slogan was not only attacking people of faith, but also irresponsible because it didn't specify how one should enjoy their life, meaning people might take it as an endorsement of any attempt whatsoever to gain pleasure, whether it or not it be moral or legal. There's not much to say about that particular point, other than it reminds us once again that there is no argument so fucking stupid that the internet will not feature someone who espouses it with all the conviction of the Sermon on the Mount.
 There are probably a lot of other descriptions you could add to that brief list, but I hope you get my point.