Well, actually... there is no way to be un-baptised and there is no way to stop being a Catholic once you became one. You'll always be "lapsed" or "excommunicated" or whatever, but there's no running away.
It might have basis in actual experience - just look at Scorsese. For what it's worth, in my experience (and in the experience of various people I'd spoken to) it really makes a change inside a person that I believe is very difficult if not altogether impossible to undo.
I always thought this was kinda cool, though.