There's an old saying about trying to idiotproof things -- they always manage to invent better idiots.
Draco/Harry or Snape/Harry pairings are simply painful in an "I will gouge out my eyeballs now" sort of way. It isn't worthy of rising to the level of something that disturbs me.
I only read the stuff that displays basic competence in grammar and plot coherence. That rules out the vast majority of weirdly-demented love scenes.
So yeah. Evil Dumbledore is alarming because it appears in writing that is worth touching with a ten-foot-pole to begin with -- and because it makes a fair bit of sense.