Having people go out and "take revenge" on innocent sea creatures, because one of them acted in self defense, is just downright stupid. Hopefully the 10 that were killed, were done by the same group of idiots, and they are caught and severely punished.
As for the footage, since his family turned down an offer for a state funeral, and went for a small private ceremony without the media, it must be quite clear they don't want his death turned into a media circus, which releasing that footage would do. I could understand if parts of it were released, that showed how big the ray was, and how close he was swimming next to it, but not the attack itself. And there's no real need to see it. Just knowing they can kill people, should be enough warning not to swim near them.