I must have a thick skin. I didn't find the tone of the article to be grossly offensive. A little provoking, sure, but that's to be expected considering the medium and the intended audience. He generalizes, yes, but that's hard to avoid in such a short article. I've read far more harsh and withering words directed at teachers and schools from people venting on this site without any fear of recrimination.
I detected more frustration with parents rather than any other attitude. I think he makes a few good points with his plea for a little respect. I find that many parents have a reflexive rejection of the idea that anyone else might have some new or different insight into their children. Parents have become so entrenched in the concept that they are the experts about their own children, they can't make room for anyone else to make a contribution if it doesn't agree with their own views. Many parents are unwilling to acknowledge that a teacher's experience and professional knowledge may have value. They don't recognize that the teacher may have a broader perspective that can be helpful on an issue.
And yes, before everyone leaps in with their stories of horrible soul-sucking teachers who refuse to nurture productive partnerships with parents, I agree that teachers should respect parents and students too. It should be mutual.