First, let me say that Matt knows this goes with the job. Heck, Matt even tweeted it saying "comes with the job." I am sure on some level it bothers him because he thought he was providing something useful and it was ripped out from under him.
Second, a lot of SEOs and Webmasters who were hurt by an algorithm directly blame Matt Cutts. He is the face of the spam team and the face of anything negative about rankings. So if a site tanks, a business tanks with it, they blame Matt. So those that were hit feel they have the right to rip him in return.
Is it right? Is it appropriate? Probably not but it is not surprising.
I say this all the time, I am surprised he can walk around at SEO events without a body guard nearby.
Anyway, the Cre8asite Forums thread is pretty heated, so you should check it out. But I wanted to create an anonymous poll and see what the group as a whole has to say.
Forum discussion at Cre8asite Forums.