Rachel Maddow reflects on the positive (yes, positive) legacy of Fred Phelps: And she's right: by embodying the worst humanity has to offer, by being so utterly and obviously horrible, he accidentally brought out the best in others.
But I think Phelps had a more insidious role: as the bigoted wingnut bigoted wingnuts could deny.
Phelps' sheer cartoonish nastiness allowed other bigots to contrast themselves with him--usually with fatuous platitudes like "love the sinner, hate the sin"--without disavowing the evil, destructive beliefs they shared. By being such an unappealing character, he made it easy for other right-wing fundamentalists to condemn (i.e., distance themselves from) him...
agreed with him on policy.
In effect, they recast the question of LGBT people's fundamental humanity as merely one of etiquette: it's perfectly okay to deny human rights to gay people, but it's just plain tacky to come out and say you hate them. Just as conservatives deny that anything short of Klan membership can be "racism", right-wing fundamentalists pointed to Phelps as the only real manifestation of anti-gay hatred. Point at Phelps to avoid confronting the sheer vicious immorality of a belief that someone's existence is inherently "sinful".
So good riddance to Phelps. He was a largely inconsequential distraction who sucked up much more than his share of the limelight. The best possible result of his passing would be a broader recognition that he was never really alone--and much more scrutiny of like-minded hatemongers such as LaBarbera, Fischer, and Franklin Graham.