Yes, most people are just taking photos of trains and doing no harm. Yes, some staff can be over zealous towards them. I bet for the most part people take photos without any hassle at all.
Staff with body cameras can't access the footage themselves or edit things to post on social media. If they could and did, they'd be sacked and possibly in court.
The problem now is that there are hundreds, if not thousands, of people who go out looking for trouble and are getting increasingly desperate to get into some trouble for views on YouTube or another platform.
Ironically, most staff are probably ignoring them and letting them get on with things - and that's why they push more and more to get attention.
As I said, eventually the people that harass and troll others are just going to cause more and more problems for the law abiding.
If you're going after people and filming in their face, you can still find yourself in hot water for that reason alone. Of course when it happens, the 'I didn't do anything to deserve this' defence kicks in.
It's the usual 'with rights come responsibilities' argument and as it stands, there are very strict rules for body worn cameras compared to Mr Magna Carter, freeman of the land, who has found a way to make a few quid instead of having a real job.