To be unable to distinguish personal abuse from criticism is worrying. I do wonder whether such people immediately resort to extreme verbal abuse in other areas of their life
I completely agree with you - they sound hysterical and unhinged. And it seems to be pretty much exclusively a Labour supporter affliction. Tory voters may think Labour policies are unworkable or unaffordable or counter-productive and that their supporters are naive, but never do they resort to the same sort of hateful haranguing and invective spewing. It's bewildering. I've seen one of my really good friends do it, all through the referendum campaign then again in the run up to the GE. She was like a possessed, swivel headed loon. I didn't recognise her. I was on the verge of blocking her completely.
I sometimes wonder if Labour supporters are actually a big part of Labour's problem in recent years, in the way that Remainer attitudes were a big part of the Remain campaign's problem. Too much negativity and witch hunting cof the opposition, not enough focus on the positives of their own campaign.
These days we are harangued by them from all angles because of social media and forums like this one. It's relentless. The stuff that's directed at us used to be confined to a heated conversation in the pub heard by six people at most, and the subject of bile venting probably wasn't even there to hear it. Once you left the pub that conversation ceased to exist, except as a vague memory once you'd sobered up. Not like today. 
Now half the country gets told daily and very publicly that the other half (or rather less than half as it turns out) thinks we are all a bunch of fascist, toffee nosed cunts or uneducated racist plebs who don't care if babies starve and disabled people die in the gutter.
As a way to make friends and influence people it's not really a winning formula.
And I think for many people, it has started to feel like it is actually the Labour Party speaking directly to them, rather than just some sanctimonious little gobshite with Marxist pretensions on Twitter.