So what? Caveat emptor has no place in honest, trustworthy business practices.

From a GDPR perspective, for anyone who is able to lay claim to GDPR protections, it wouldn't matter whether this is written in red on the first line of the agreement - "data protection by default" means that you must default to not sharing with an unlimited number of people.

What this means in practice is you can't default anything containing personal info to being public by default.

Yup. One of the best benefits of GDPR is that you don't have to read the fine print anymore, because companies can't legally put anything abusive in there, at least with respect to processing your data.

Absolutely. Article 25(2) is written for this specific situation, and expressly prohibits opt-out situations where personal data might be made publicly accessible:

"In particular, such measures shall ensure that by default personal data are not made accessible without the individual’s intervention to an indefinite number of natural persons."