Agreed, the rules should be applied selectively and at random
1. she was allowed to board with the stroller, neither you nor i know why, however; anyone who has every flown realizes that before entering the plane she passed at least one, and possibly as many as four points where airline or security personnel had the opportunity to review what she was planning to carry on the plane. any of those points would have been an appropriate time to advise her that she couldn't take the stroller aboard and to provide her with other options. it is not the passenger's responsibility to know and enforce the airline's rules. that airline employees either didn't do so earlier is not her responsibility or her fault.
2. there are probably some times and circumstances where it is advisable to physically wrestle a stroller away (i'm assuming this is what happened, but maybe she was compliant and the dude was just clumsy as eff and hit her turning around or some crap, who knows. it's pretty obvious from the video, though, that the other passengers blamed the fa and not the woman) from a woman carrying a child in her arms, at the risk of striking one of them. her having boarded a plane that has nowhere to accommodate the stroller, and you not wanting to deal with it is definitely not one of them.
btw, i've been on planes where people have had children in strollers, so i dunno if this assumption that she have known a stroller was verboten is accurate.