[iudqnolq]

I've heard people argue that that effect isn't a nudge, it's deceit.

That is, all you're doing is tricking people who didn't read carefully. People don't know they've opted in and would opt out if you called and told them that they checked the box.

I find it generally plausible that defaults don't matter much for what people consider very important decisions. I have minimal experience in this area, though.