Having only watched Buffy years after it aired, I'm totally oblivious to conventional wisdom along the lines of the sixth season being terrible, and that being attributed to Marti Noxon. I liked that season and didn't know anything about Noxon, though she always seemed good on DVD commentary tracks, and I've noticed her name in the credits for other shows I enjoy somewhat.
Do agree that it is disconcerting when one's fellow fans appear to Totally Miss The Point of something. The endless parade of homophobic, sexist, and just generally reactionary comments in the letters section of the Buffy comics really threw me for a loop, but then again it's baffling to me that someone approaching the show from an explicitly feminist perspective didn't like season six, so there's no accounting for taste, is there.
We all want the people we admire and care about to like the same things we like, but more often than not, they don't. And likewise we'd like all the people who do like the things we like to be admirable and care-worthy people, and to like those things for the same reasons. But they also don't!
And it's okay, and at the end of the day there's no reason why any random fan of whatever thing you're a fan of is going to be any more or less likely to be a good or decent person than any random person who isn't a fan of that thing, but in any case "season six was good" is doubtlessly a stronger debating position than "season six was terrible but it wasn't Marti Noxon's fault," and so I do recommend giving that season another chance.