nah, let's go hunt for rare-earth elements left over from the creation of the solar system out where we aren't in danger of stressing an already stressed ecosystem.

Let's pay the tremendous up-front costs of lifting mining operations out and reap the long (caveat: very long) term benefits of doing so.

edit: In case that came across as sarcasm, I am in dead earnest. Whatever the relative costs of so-called asteroid mining versus deep sea mining, the ecological cost tips the balance waaay in the favor of asteroid mining. It's just that we'd have to have a longer-term mindset than we currently do.