I can quite understand the frustration felt and even sympathise: Crew also regularly travel in economy (contrary to perception, we are not usually upgraded, especially when travelling with another carrier) and experience precisely the same issue. An FA cannot intervene if the customer in front is simply reclining their seat, thereby using a facility offered by the airline and paid for by the customer.
My issue is that the behaviour described is physically aggressive and highly likely to lead to some sort of incident in the cabin. It is unlikely to achieve anything except to cause distress to those surrounding and risk escalation to some form of more serious incident. If people feel that this is an acceptable method of expressing dis-satisfaction, then so be it. I'm afraid I don't.