When signing up for a "free" service, I basically assume all data entered will be used for advertising / marketing purposes. This is a safe assumption to make.
I don't disagree, but I think we should still be able to get upset when a free service uses the data for something other than what they said it would be used for.
It's why I love GDPR. Since it requires explicit, opt-in consent, I can just register or visit a site and don't worry much - abuse of my data is a bigger risk to the service than it is to me.