I've never witnessed violence toward teachers personally (I am one), but I'm sure it happens. Coarse language no doubt, but that's probably nothing new especially in middle school and up. I have some friends that teach elementary school and they say you wouldn't believe the vulgarities that come out of kids as young as 1st grade. The article in the OP definitely rings true that staff can basically do nothing when a kid flies off the handle other than follow him around, maybe stepping in between if the kid goes after another kid; personally even then I'd think twice in today's world. Any fear of consequences or discipline is basically absent in kids that continually get in trouble because there's little a school can do any more.
You definitely hear a lot from the elementary crowd how certain kids have these meltdowns where the rest of the class basically has to vacate the classroom, sometimes multiple times a day - that's total BS that the other kids have to have their education negatively affected constantly. I know some veteran teachers who say this has really escalated in the last several years and was something basically unheard of 15 years ago.
As far as parenting, most are good enough. There certainly are some that have no control of their kids and make excuses for them. As with most things, it's 5% that cause 95% of the issues. A vast majority of the time, the kids with lots of behavioral troubles in school come from broken homes or at least chaotic homes.