You don't need to block someone to end a conversation. Just say "you're acting in bad faith, and I'm done here", then stop replying to them. They'll most likely reply to you once or twice, and that'll be it. And if you use kbin's block function, you'll never even know.

If you're engaging with someone who is acting in bad faith for that long, you're most likely trying to convince the audience that the other person is wrong. If the fact that they're arguing in bad faith 10 hours in isn't abundantly clear to any person with half a brain reading your thread, then maybe they're not acting in bad faith and they just disagree with you on something you feel strongly about.

Also, you kind of said the quiet part loud there. "Engaging in bad faith" isn't, in and of itself, the same as harassment. I'm sure that there are individual communities on kbin where critics of particular ideas and ideologies are silenced, and if that's what you need in order for your ideas to stand, then I'd suggest staying in those communities. The general consensus here seems to be that if you're out arguing in public and someone isn't actually harassing you (even if they disagree with you in a way that you believe constitutes "bad faith"), then they should be allowed to speak. Reddit's toxic climate has just been exacerbated by their bad block feature, because now the motivation when you get into an argument is to be the first to block so that you're guaranteed to have the last word. It doesn't lead to useful discourse.

Bare minimum, if you want block to function this way, then you should have to delete any un-replied-to comments of yours in order to be able to do it so as to remove the perverse incentive to abuse the feature to "win" arguments. I'm sure you'd find that agreeable?