While a certain percentage of various types of mammals might be demonstrably homosexual, I doubt that anyone can argue that homosexuality is in any way a positive trait when viewed evolutionarily.
What does that have to do with tolerance? So let's recap: you think that it's ok for parents to teach their kids that homosexuality is wrong because from an evolutionary perspective, it offers no advantage? It hardly gets more idiotic than that.
The reason why it's wrong for parents to do this, is because being homosexual has nothing to do with right or wrong. To use your own demented analogy, if someone is born without a limb, it's not wrong...or right. It's just the way it is, and that person should be accepted.
Homosexuality would only be wrong, if you try to map it to some bronze age religious dogma. Homosexuals just drew a different card from the nature deck, and they are just the way they are. It's not wrong, or right. It's just their nature.