First and foremost, just because you saw something on youtube doesn't mean cops are going to pursue it. Has that stuff been filmed ? Yes, have people gotten away with it ? yes... Have people been arrested for it ? Yes. They have, there was a thread on that in our OT a few months back, where a man pulled an Oscar out of a tank (his GF's) and stomped it to death. He got animal cruelty charges.
Second, about the wolf/deer... Why not ? its nature. Things eat other things. There's not much difference from a wolf eating a deer and what i've said, aside from gore. And if gore is what you're talking about, then that makes P's eating fish even more mild then a snake eating a rabbit, most people aren't stunned by fish being ripped apart and this discussion is tailored towards all people, not just fish keepers.
In the end I just disagree. Any animal killing any animal isn't that bad. If they were animals that would never meet in the wild, ok thats different.