I really have no problem with them being 'assertive' with people who have no ticket / wrong ticket / someone elses free pass etc etc etc. In fact I am often delighted to see the offenders nabbed and put in their place.
However, I do not think they should be quite so 'assertive' in their manner to us 'law abiding' passengers with valid tickets.
There has to be a happy medium.
I can't remember the last day I didn't train.