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IANAL so I can't address most of your questions, but

> When I cite you, must my posts be deleted as well ?

You mean for comments and such? What I write on a site's comment section falls under copyright law, with the usual attribution reservations etc. So no.

> Banks and maybe even insurance companies have already the right to know much about you.

I shouldn't have used the word "privacy" in my comment. I think calling GDPR a privacy law is a shortcut a lot of people take (myself included), but it really is a data protection law. (It's even in the name!)

GDPR doesn't talk about privacy very much. In fact, I just searched the full english text of the law: There isn't a single instance of the word "privacy".

In other words, it doesn't so much say who can and cannot store and analyze your data. Instead, it lays out your responsibilities if you are storing/analyzing personal data, and your (consumer) rights as someone whose data is stored/analyzed somewhere.