Earlier quoted context omitted.
One problem with making misinformation a bannable offense on Twitter is that they'd have to ban so many mainstream journalists. (Seriously, it's obnoxious how many totally bogus viral claims they start and spread on Twitter; some combination of wide reach, trust, and never bothering to verify anything they post on social media.)
Cite an example of a mainstream journalist propagating a viral claim that any reasonable person should have known was false? That's what misinformation networks do.
Edit: let's have a look at https://twitter.com/afneil/status/1001158920663109632 - Andrew Neil is Chairman of the Spectator (important "serious" rightwing politics magazine) and a BBC presenter. He's accusing the NYT of "Stalinism". One of these has to be wrong.