Moral relativism in general is a desperate pseudo-ideology made to rationalize hedonism. The people who adopt it only half believe it. Taken to its natural conclusion, rape and murder are totally cool as long as the person committing these acts believes they are morally right. The average normie nihilist is apalled at the full implications of this philosophy so they arbitrarily pick and choose where they want to apply it, generally believing it applies only to their particular vices.
There is a very simple and ancient philosophy which ultimately matches up with what we know about the human brain. Pleasure and pain balance, or at least your perception of them does. If you become desensitized to one extreme, you become more sensitive to the other. This concept also helps explain the development of degenerate sexual fetishes where people feel the need to mix the two just to be able to feel something again.
In short, degeneracy will not make you happy. It will make you a better consumer, it will make you want to chase after more and more temporary thrills in order to distract yourself from the vacuous abyss that you have turned your life into, but it won't make you happy.