Yeah, liking Family Guy really wasn't something that earned someone scorn until Seth MacFarlene hosted the Oscars - he kind of invited all of the barrage of criticism he's gotten since then given he had an opening monologue that referenced George Cloony sleeping with a 9 year old.
I used to like Family Guy, but like a lot of other folks mentioned, there was just a point where it seemed like the show stopped trying. The jokes were rehashed or fell flat, the characters made even flatter, the humor got imbecilic, and the politics pushed got way to preachy. Toss in the fact that it seemingly got worse and worse with every passing season, and in spite of this, got two barely distinguishable spin offs and has episodes of each syndicated on at least four TV networks at any given moment, and a backlash was inevitable. It's telling that we've already seen Cleveland Show and American Dad canned and the backlash against Family Guy/MacFarlene is only growing stronger, given there are already calls to pull his sitcom from the air. The time between Ted and hosting the Oscars will likely prove the peak of MacFarlene's career.
Thing is, MacFarlene isn't without talent - one of my favorite cartoons as a kid, Johnny Bravo, had a heavy influence from him, and the early Family Guy stuff was utter brilliance. Problem was, once Family Guy got brought back, let alone become a billion dollar media franchise, he basically could do anything he wanted, and for lack of a better way of putting it, he got lazy. Maybe he's still got some brilliant work in him, but it's certainly not coming out in Family Guy.