Which in most public speaking venues will get you thrown out, and if you do it in the open air badly enough you can also get arrested. (America is rather unusual in the amount of this it allows, not always to the good)
And if we look at this particular case it's not "booing", but "Over a period of three months .. cruel campaign of vile racist abuse".
Also: "You are currently serving a sentence of 40 months imprisonment, imposed on 17 the December 2015 for stirring up racial hatred against the Jewish comm unity in Golders Green. That offence was committed whilst you were on bail for the present offence, which in turn was committed whilst you were on bail for other offences of sending malicious communications over the internet and harassment." -- I think maybe this guy should not have been allowed Twitter while in prison.
Oh just read the whole thing on aggravating features:
1. This was extreme racial hostility over a prolonged period, 3 months.
2. There was careful planning.
3. The offence was part of a pattern of racist offending.
4. You were acting, in effect, as a member of a group promoting racist activity.
5. The impact on Ms Berger was very considerable.
6. As a Member of Parliament she was providing a service to the public.
7. The offence was committed whilst you were on bail and awaiting sentence for other offences of hate crime committed over the Internet.
But if twitter is a public, open platform with global reach then you will also get people who react to you like a public speaker. Which includes things that do not meet the legal harassment standards. Just the texual equivalent of booing, hissing and throwing insults at people to get them off the stage.
And I think people need to be aware of this when they state political opinions on the global twitter soapbox instead of doing it among their friends.
I'm sure changes can be made to dampen it. But this is the current situation. And I'm not sure harassment is a good way to describe it.