Philosopher Roger Scruton thinks the bus ad means this:
The new humanism “seems to have no consciousness of what is clearly announced between the lines of the text [ON THE ATHEIST BUSES], namely that there are no ideals higher than pleasure.
But philosopher Stephen Law counters Scruton with this interpretation of the bus ad:
“Don’t allow, as so many do, belief in God and his divine plan to blight your life (through endless recriminations about your sexuality, about a “woman’s role”, etc.). Contrary to what most religions tell you, this is the only life you have – so make the most of it!”
Law discusses these contrary readings of the bus ad here.
My impression, on first hearing the slogan, was closer to Scruton’s. I thought that it was saying something essentially frivolous and sunny, as if to say: “There’s probably no God—now go have a nice lunch and all will be well!” I thought that it was contrary in spirit to the types of honest atheism once espoused by pessimistic writers like Albert Camus, who would not (in my view) have downplayed the difficulty or absurdity of living in a world that functions without telos—and is more akin to a chaos than a cosmos. I think that an atheism that does not acknowledge fully the role of the ABSURD in human existence (both with or without a god presiding over it) is, ultimately, a dishonest and shallow atheism.
In other words, removing God from the equation of existence does not make life less existentially anguishing. It simply opens up a whole new set of problems of equal and difficult import. The distance between “enjoyment” and unhappiness is not bridged by a singular act of ELIMINATION—by removing God from your life.
Still, I can see Stephen Law’s modest and sensible interpretation of what the bus slogan was meant to convey, and think that IF read in this narrow way, the slogan is a good one. But I think that Roger Scruton’s old style humanism (which he describes as that of his British parents’ generation) is, perhaps, better. Scruton suggests that his parents’ version of humanism would have been put this way:
“There probably is no God; so start worrying, and remember that self-discipline is up to you.”