Are you really being that technical, or have you not been hearing about the ivory trade as it exists today?
Regardless, the OP is missing a critical point. Zoo animals have something many humans don't have.. A job with benefits.
Ivory has been outlawed for use in piano keys for nearly sixty years. Six decades. Using that in an argument against the ivory trade is ridiculous. It might seem to be of great importance to somebody that is uneducated but to use it with anyone that is aware would pretty much negate anything else you would have to say.
As far as the ivory trade today and animals and all other things emo related, I have nothing to offer. I think we have a lot of major, major problems in our nation and I prefer to devote my attentions to those issues. But I won't stop you from doing what pleases you.