The trouble with the "new atheists" is that their moral outrage, most recently voiced against Papa-Ratzi during his state visit to the UK, is ultimately built upon the shifting sands of moral relativism. When they take the moral high ground they need to presuppose theism at the same time as they deny it.
The implications of the denial and disappearance of God for morality were drawn out forcibly by the atheist existentialist philosopher Jean-Paul Sartre (1905-1980) in a lecture that he gave in 1946. Sartre's eyes were wide open to the implications of atheism, and in his following words he doesn't try to hold on to or smuggle in a morality that depends upon the existence of God.
It is somewhat ironic that the "new atheists" have not caught up with the insights of Neitzsche or Sartre. Perhaps the explanation of that irony is due to a lack of interest in philosophic literature and rigorous philosophic thinking. It is also due, I have no doubt, to the vanity of trying to re-write the rules of the universe.
When we speak of “abandonment” – a favorite word of Heidegger – we only mean to say that God does not exist, and that it is necessary to draw the consequences of his absence right to the end. The existentialist is strongly opposed to a certain type of secular moralism which seeks to suppress God at the least possible expense.
Towards 1880, when the French professors endeavoured to formulate a secular morality, they said something like this: God is a useless and costly hypothesis, so we will do without it. However, if we are to have morality, a society and a law-abiding world, it is essential that certain values should be taken seriously; they must have an a priori existence ascribed to them. It must be considered obligatory a priori to be honest, not to lie, not to beat one’s wife, to bring up children and so forth; so we are going to do a little work on this subject, which will enable us to show that these values exist all the same, inscribed in an intelligible heaven although, of course, there is no God.
In other words – and this is, I believe, the purport of all that we in France call radicalism – nothing will be changed if God does not exist; we shall rediscover the same norms of honesty, progress and humanity, and we shall have disposed of God as an out-of-date hypothesis which will die away quietly of itself.
The existentialist, on the contrary, finds it extremely embarrassing that God does not exist, for there disappears with Him all possibility of finding values in an intelligible heaven. There can no longer be any good a priori, since there is no infinite and perfect consciousness to think it. It is nowhere written that “the good” exists, that one must be honest or must not lie, since we are now upon the plane where there are only men. Dostoevsky once wrote: “If God did not exist, everything would be permitted”; and that, for existentialism, is the starting point.
Everything is indeed permitted if God does not exist, and man is in consequence forlorn, for he cannot find anything to depend upon either within or outside himself. He discovers forthwith, that he is without excuse. For if indeed existence precedes essence, one will never be able to explain one’s action by reference to a given and specific human nature; in other words, there is no determinism – man is free, man is freedom. Nor, on the other hand, if God does not exist, are we provided with any values or commands that could legitimise our behaviour. Thus we have neither behind us, nor before us in a luminous realm of values, any means of justification or excuse. – We are left alone, without excuse.