Agreed. Anyone who you'd ordinarily want to blacklist should definitely be on your automatch blacklist. But the reverse might not necessarily be true. That is, you might want to only "automatch blacklist" someone who you'd be happy to play with, but who has a habit of turning on automatch and then wandering off.
I haven't quite decided how to implement it.
I'd like to be able to have a temporary blacklist, so if I say no to a game, that no sticks for some time. That could be like for an hour or two. For the wandering-off player that means you just have to say no once when you notice they don't answer. But also otherwise your preference to not play a particular game might be more or less temporary. Say, you just want a relaxing game before bedtime, and think that if you play against a particular player it will instead be a prestiguous death match with no relaxing qualities.
I would like the ordinary "no" to be this function. When you say no to a particular game that otherwise fits your automatch criteria, it's probably because you don't fancy playing that particular player right now, so avoid suggesting the same matchup again soon.
(This may sound like I'm cherrypicking a lot with automatch, but I don't. In fact I don't think I have said no except for people who didn't answer for a long time. But I did refuse sometimes on Isotropic's automatch, mostly when I had just played that player and I didn't like that for some reason. I didn't learn the names of those, and wouldn't have bothered with a permanent blacklist, but a temporary no-thanks would have suited me fine then.)