When the U.S. purchased the Louisiana territory from France, it basically doubled the size of the country. And after that, we bought Alaska from Russia. Both of those purchases turned out pretty well for us.
Granted, Russia probably regrets selling us Alaska. But Napoleon managed to dump territory he couldn't defend and raised cash to wage his wars of conquest. I'm sure he was glad he sold that territory … right up until they locked him on Elba.
So, I just don't see the big deal. We ask the Danes if they want to sell Greenland. If they don't want to, they can just say, "No."
The only think close to an answer from The Left seems to be, "He should have known Denmark wouldn't sell. So he must be a MORON!" Well, that's silly. You don't know for sure until you ask. I think if you'd really stop and think about it objectively, you'd realize that. Not that I think we SHOULD buy Greenland unless we can get it on the cheap. But again … you don't know until you ask.
I'm going to give BA to the person who represented The Left's viewpoint POLITELY. Once you accuse those who disagree with you of being morons or stupid, that seriously reduces your chances of getting BA.