The only reason you guys are mad about this is because Trump cancelled it. If some administrator over at NASA canceled it, nobody would give a shit.
Err.. Ori, you can't say that. I mean, seriously, that's beyond your powers of deduction unless you're the Omnissiah. Personally, here's my rubric for determining whether I dislike something just because Trump did it. I replace every instance of Trump's name with General Mattis. If that suddenly makes the proposal seem like a sensible thing, as it did with the Syria strike, then I will admit that I'm biased against Trump and that's probably a fine idea.
I, like others, oppose the Keystone pipeline for a variety of reasons, but I'm willing to let that go as one of those 'the parties must compromise' issues. We got healthcare last round, the Republicans deserve a concession for something they want.
Then we come down to things like the Wall, the breaking of the Paris Accords, the repealing of environmental protection acts, and a half-dozen other incidents that I would oppose regardless of who advocated them. As far as the asteroid capture goes, that's something we're going to need to do if we're going to leave the fragile cradle of the Earth. Yep, the mission was expensive and would likely bring back a hunk of rock with a limited yield of the really nice stuff- yet it would show we could.
The plane the Wright brothers flew stayed in the air for seconds. I don't know if I can change your mind, but we need to keep pawing at space. We need to work on orbital construction, and unless we miraculously find a way to send materials up from earth much more cheaply, that means orbital mining. We can't expect a colony when every resource has to be shipped in from foundries on earth. Small expensive steps.
tl;dr: We don't all hate what Trump does just because he does it- but we're damn concerned about where things are going.