The concept of a fish thriving in the wild after living in an aquarium is too often idealized by people who choose to believe its like releasing a healed bird nursed to health after a broken wing. It's been awhile but I keep bumping into people that say they just let their oscar or pacu go in the local lake. They probably a) destroyed the environment and b) did it all in an hour before dying. I can understand not wanting to eat a longtime pet like my 14" pacu that my best friend offers to cook for me everytime he's over. We all need to keep in mind that it's been a privledge all this time to own fish and privledges get taken away when things like the enviorment suffer because of a careless mistake.
Conversly, different entities like Green Peace don't always know what exactly mother nature intends or would enjoy. A whale was found in the same Mississippi river as the goldfish closer to Arkansas than the gulf. Whales aren't that common to the gulf. If I remember correctly, they mostly stay in the Pacific.
Another contradiction is that even planning euthanization isn't fullproof. There are plenty of nonnative animals and fish all over Florida that entered the wild during hurricane flooding and continue to do so in more states/countries than Florida. If this becomes the cornerstone for the argument they we all are in trouble. I'm hoping the powers that be recognize odd whale sitings and even octopus as upstream as Montana or sharks swimming far in land to keep in mind that it's going to happen anyway.
My 2 cents.