It's a lesson people have to learn periodically, I suppose. As noted in that FAQ, both Frank Miller and Alan Moore already went through this with them, publicly and loudly. I like his point about not knowing what was lost by poisoning those relationships. They robbed themselves of the fruits of two of the best writer/artists in comics history, at the peak of their creative ability, and robbed us of seeing what they'd have done if they'd stayed.

(Frank Miller at least did more work for DC later, but sadly not at his peak)