When there is a viable artificial alternative, in this case space habitats, I think terraforming is inexcusable.

Okay, but why? Particularly in the case of Mars, which doesn't presently have an extant ecosystem.

Why increase the productive capacity of Mars if there is literally no reason to?

I mean people usually do not engage in extremely expensive infrastructure projects for the meme of it. That's precisely why NASA said that we can't do it, and should bother. The question is why you have a moral, rather than simply practical objection to this?