[B-Con]

What if it's malicious?

Eg, "I hate your political ideology. I'll unsubscribe you from the site you forwarded me an article from."

I'm sure that kind of threat is minimal and easily corrected, but the OP's suggestion of hiding it somewhat addresses that. It doesn't eliminate the threat of course, but it doesn't put it under their nose.

[monochromatic]

A confirmation email with an "undo" link fixes that problem as well.

[mikegreco]

This seems like an extreme edge case as far as problems go, and can be absolutely infuriating when a user doesn't want to get mailed anymore.

[emn13]

One extra mail for an explicit user action? It doesn't sound very infuriating to me. and if it is, well, at least they won't hear from you again.