Note that this would be... Well, stupid. People sometimes opt in for newsletters they care about and with this scheme they would opt out. Not only that, you would get tons of "subscribers" who explicitly don't care for your mails.

I am not arguing that dark patterns don't work in general, I just don't think this is a good example.

My interpretation was that the box just doesn't do anything; i.e., you can click it or not click it, but either way, welcome to the news letter mailing list.

Maybe I was wrong.