You see a teammate fighting someone 1v1 and they win. Result: you get yelled at for helping.
You see a teammate fighting someone 1v1 and they lose. Result: you get yelled at for not helping.

Damned if you do, damned if you don't.

That being said, there's plenty of idiots in BG's that pull that crap of trying to get the most HK's. It's annoying and I have to calm myself down sometimes when playing. Sure am glad you hopped in to "help" me kill that guy who was at 5% health and running for his life, there's no way I could have have taken him down myself!