> I understand that the diamond trade has a vested interest in differentiating, but why would end consumer care?

Because for some consumers, the scarcity (artificial though it may be) of mined diamonds is what they are buying for.

And because for other consumers, ethical concerns that favor artifical diamonds are what they are buying for.

In either case, knowing that you are getting what you want and not something else is a concern.

> This is a purely emotional response.

Value is always subjective and largely emotional.