That's not how it should work. You could just go fish for anyone's data on the basis that he had a relation with someone that broke the law.

Data should be protected just like the intel you are giving to your lawyer or your doctors. There is absolutely no reason a government should be able to simply catch your data without a reasonable cause.

Knowing someone is NOT a reasonable cause. If they had proof that he did something that's a different story, but then they'd just catch him wouldn't they?

> You could just go fish for anyone's data on the basis that he had a relation with someone that broke the law

I believe what you're describing is the way the Prohibition-era gangs were broken up. It's a long-standing policy that this is acceptable policing in the US; it's not generally considered a fishing expedition if police investigate a person who associates frequently with a person they're building a criminal case on.