I went to uni and studied an engineering degree. I was also a reservist in the army at them time and spent the rest if my spare time walking with the associated uni club or messing about with computers and occasionally drinking down at the students union.
Strangely I am sure that if you did a study of students engaged in 'social justice' activities I think you would find a relative scarcity of engineering and science students and rather pronounced over represtation, proportionally, for thoose studying various humanities and a particular over representation in thoose studying under the umbrella often labelled 'grievance studies' by its critics.
oops, thought it was bert... as even the humanities students dont all flock around the Union affairs, yes they're disproportionately involved and that makes it a rather stale atmosphere, but it's not some massive army you purport it to be. Most Unions have serious trouble getting 20-40k students interested, at most they'll get around 10% if incentives are laid down. (This may be different for newer universities with a heavy humanities focused course delivery)
It'd be a damn sight better for students to actually partake though as the decisions made by the biased student body end up being utterly pointless, even to the point of totally changing their mind afterwards (too late mind you), frustrating ***** honestly. Most of them do it just to get the free year off of responsibility though and an extra year at Uni.
Certain societies are also just loud and almost barren in membership (could just be a case of too many societies though and overlapping interests), i may be biased though as i don't know how it's like at post 1970s unis.
This is honestly just an American thing i feel, importing a grievance that isn't even relevant and making it out to be a massive horde of evil commies, is just unfunny.