I'm with the "Why/How can a 4yo get through a fence into the enclosure?" crowd.
Parents should keep an eye on kids, but 2-4yo's can be quick. How many get run over in driveways or drown every year because someone "turned my back for a second"?
Still sucks they had to kill the gorilla. :(
And I don't agree with the stupid petition.
Kids are weird. You can be the worst parent and the kids survive despite complete negligence. You can be the best parent and the kids can end up in a very bad shape.
Until we know exactly how the kid did what he did we can't really say.