A guy has a right to express an opinion about a share, but it gets tedious when he repeats proven nonsense over and over again.
More importantly, he doesn't have a right to be deliberately insulting and obnoxious. Equally he can't expect to be a persistent and malicious liar without some retaliation from civilised society.
The guy has no concept of civilised human interaction and since he clearly can't or doesn't want to mend his ways he has to be excluded from civilised discussion - even when some of the points underlying his invective may have some merit.