Defaults very clearly work in matters such as consent to organ donation. In countries where you need to opt out of organ donation, few people bother to do so.
Another question is whether this increases the total amount of successful donations. I was looking around for studies and found this one [1], which basically says "in some countries, yes".
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.
There is also some research suggesting that defaults in organ donation (so called presumed consent) may decrease rates of actual donations in those countries. I can't find the original podcast where I heard about it (I assume related to either Planet Money or Freakonomics), but found this source:
That's not a conspiracy. When two companies, or countries, or individuals have business dealings on many different levels, a lot of things can be negotiated at the same time.
Another question is whether this increases the total amount of successful donations. I was looking around for studies and found this one [1], which basically says "in some countries, yes".
[1] https://behavioralpolicy.org/wp-content/uploads/2020/01/Does...