Thank you! Someone needed to make this post.
I can sort of understand why some people don't like granting undos, but I personally think that having fun and seeing who's the better Dominion player (or who's more lucky) should take priority over winning, especially winning over a misclick.
Actually, I have 2 people on my blacklist (I know it would be bad to say their names in public) who both denied my undo request after I accidentally played my Coppers when I wanted to buy Grand Market. Both are in the top 1000, and one is even near the very top, around place 20 or 30. I'm not rooting for anyone to fail, but please, tell me they didn't get so high up by preying on misclicks...