After a show at Orlando's SeaWorld, the killer whale, Tilikum, pulled a trainer into the water and kept him under water to death (2010-02-24).This is not the first incident that Tilikum played a role for people's death. In addition, it is reported that Tilikum showed a frustrated behavior before the show (from CNN).
Jane Velez-Mitchell at CNN maintained (from CNN) that whales should not be kept captive under the cover of science, the realism of which is about profit.
As long as my knowledge goes, wild killer whales never attak human.
While it is wildlife conservation to rescue stranded or hurt whales, it is hard to be justified to capture wild whales to put them on a show.