Are you sure those people are stupid (ie. they care about the environment and want to do the right thing but mistakenly do the wrong thing instead) or simply putting their personal convenience above the convenience of others? To be stupid, I think it would have to be an action that goes against their own interests.
Tragedy of the commons isn't caused by stupidity but by selfishness. It's different.
It does go against their own interests when feeding animals is more likely to attract dangerous animals that attack tourists.
People don't always make the decision they know to be in their best interest. If they don't actually know what's in their best interest, then I'd say it's less an issue of stupidity and more about ignorance.
Attack other tourists. If you feed a duck then leave, you're not attracting a bear to attack you personally. You won't step in your own poo either. Somebody else will.
Tragedy of the commons isn't caused by stupidity but by selfishness. It's different.