Is this guy a political dissident or something?
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?
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.