IMO, if the argument against the riot PKers is "I don't like it!" (which is the case 99% of the time when people complain), then there's zero substance to it. If the actual concern is that it's trapping new players and making the experience less enjoyable for them, then there might be. Those 60-person riots at the bridge have probably been doing the latter.
I'm a supporter of letting people play the game the way they want to and enjoy it however they please as long as it doesn't harm the game or other people. I don't believe in telling people the way they PK is "wrong" or forcing them to PK a certain way just because others have brainwashed them to think that there's a correct way (just because it's their preference).