Well, I suppose ultimately it depends on your perspective if you agree with the animal rights protests. I think, given your response, you don't agree with them (and to be honest I don't ether although it's a complicated issue that I don't think I really have the answer too). But seeing it from their angle: Keeping dolphins in captivity is wrong, they want to free the dolphins, this is a good chance to do so but they don't have a legal way of forcing the park to do so, however, if they can get a good protest going and turn public opinion against keeping them in captivity, maybe they can free them, which, remember, from their point of view is a very very very good thing. However, from their perspective the zoo duplicitous snuck out the dolphins under cover of night in an attempt to avoid any chance of backlash or public opinion. I think, idk. It makes sense to be angry if you ultimately agree with the animal rights activists. "Private corporation being private" Is not an excuse really when you think they are still ultimately being evil.
Seen from the other angle, that keeping the dolphins in captivity is right, they cleverly managed to avoid meaningless harassment. Ultimately... Well, I can see the argument both ways here.
Edit: Obviously that's a generous assessment for the animal rights activists mindset, that they've actively decided that this is a case of the dolphins not belonging in captivity and needs to be specifically stopped, and not just "We do protests. Damn we missed a chance to protest." And also a generous assessment of the parks mindset, that they've actively decided that this is a case of the dolphins belonging in captivity and needing to stay in it, and not just "Lol, of course we're gunna sell these blowhole motherfuckers off, now how can we do it with as little attention as possible?" But I guess without further information I'm fine being that generous.