I went to my first ever left wing demonstration in, I think, 1977. In over 30 years I have never heard of people being chased off demonstrations, having their placards ripped up, or being told they could not march on the same demonstration as the rest of the people there. Never. And this is despite people having many weird and wonderful, and frequently, to me, objectionable slogans on their placards or being chanted through their loudhailers. It has always been accepted as just part of *having* a demonstration that there will be people saying things you don't like.
(An exception would be if there were fascists of the BNP-type marching. I don't remember ever being on a demo where this was a real issue).
That the left now apparently thinks nothing of ripping up placards just because they disapprove of the slogans, or 'chasing people off demonstrations' is deeply, deeply disturbing, and if you are 'considering joining in', it's you who should be asking yourself very, very searching questions.