[g-b-r]

Just as in personal relations, sending a final message rather than ghosting can be uncomfortable, but that's not an excuse not to do it.

If/when you don't want to interact further, just say it (hopefully stating the reasons, such as that the hiring process is imperfect, but the company can't devote infinite resources to it); after you did that it's completely fine to ignore further inquiries.

[joshstrange]

This is exactly what I did. Everyone got an email no matter how uncomfortable, I would engage 1-2 emails past that then make it clear that I wasn't going to reply again.

[Shorn]

How often would you say you got these negative interactions (anything other than a "thank you" or silence)?