"I had motives for not wanting the world to have meaning; . . . The philosopher who finds no meaning in the world is not concerned exclusively with a problem in pure metaphysics;
he is also concerned to prove there is no valid reason why he personally should not do as he wants to do . . . For myself, as no doubt for most of my contemporaries, the philosophy of meaninglessness was essentially an instrument of liberation. The liberation we desired was simultaneously liberation from a certain political and economic system and liberation from a certain system of morality.
We objected to the morality because it interfered with our sexual freedom."—Aldous Huxley, "Confessions of a Professed Atheist"
A bow to Mr. Huxley -- and you just knowingly sucked me right into this, did you not?
he is also concerned to prove there is no valid reason why he personally should not do as he wants to do . . . Because man, at his most basic, is a social creature. Humans need the company and cooperation of other humans to survive ("No man is an island..."). When we "do as we want" we run the risk of alienating our supporting group -- a situation that we instinctively know could be fatal (even if modern technology means it won't). When one is that deeply tied to the group one develops a set of rules to allow the group to interact in relative peace.