Earlier quoted context omitted.
How is that achievable? PIs can legally do it. Random people can keep tabs on you and exchange gossip. It's the sudden scale and low cost that doesn't sit well with freedom to not be tracked in public 24/7 we took for granted.
If PIs can "legally" do it then it sounds like there is a law which allows them to do it. That law can be revoked (unless the power comes from Constitution which would make it effectively impossible to revoke). Note that PIs are effectively illegal under GDPR by default. They would generally need to provide Article 13 notice, i.e. you would become aware of them unless they were just asking around without actually fol…
EU is more complicated, but Article 14.5.b allows withholding notice if it would impair/defeat the purpose of processing. The PI must however apply "safeguards", whatever it could mean.