Reminds me of blade runner.

It would take less energy to re-hydrate a entire planet than it would to go to another star and pick up the water there and bring it back, especially if you do it in a reasonable amount of time. So yes a lot of alien invasion sci-fi is just dumb.

I wouldn't want to completely isolate them. I think they should have a path to improve. I think its ok to sell them stuff like food, medicine, clothing etc. Completely isolating countries has never led to change, just misery.