No?
We're not talking about threats. We're talking about general behaviour. Twitter is a place of parody accounts, satire, criticism, mockery, even contemptuous indignation towards others. The kind of argumentative back and forth comments that float around on Twitter (and on this forum) could never be in real life, between two people. Interactions between anonymous or pseudonymous strangers online will have a lack of restraint and honesty that is implicit in our daily interactions. Just like how interactions at work or at home are distinct.
You can also always excuse yourself from, or filter out your Twitter. There are plenty of things you can do on there if you don't like being the recipient of negative comments.
Sometimes you can. If someone I don't want to talk to comes to my door, I close it. I don't let them in. If they try force themselves in, it escalates.
I have never said that death threats should be legal over Twitter. Stop bringing it back to that. It's dishonest. I've objected to your unstated premise that insults, mockery, parody and bulk mentions constitute harassment on Twitter.