I would counter that we need to make it more difficult for police to use Stingrays, but law enforcement should absolutely engage in all sorts of man-in-the-middle attacks when it is in the public interest. The problem is not that the have a particular capability, but that they have such an overabundance of them and that they deploy them far too readily.

never heard about faraday cages?

... now we just need to figure out how to lure the surveillance target into our EM-shielded cage.

my point is that it's quite easy to "play" with such things without actually breaking the law

I think you may have misunderstood the comment. In the US, Ireland, and probably elsewhere, police are using rogue cell sites ("Stingrays") for surveillance. The person you replied to is claiming that this is illegal, and the police forces that are doing it should be punished. They weren't talking about people experimenting with setting up Faraday-caged toy cell sites in their basement — there's absolutely nothing wrong with that and it should be encouraged!

They aren't "playing".

Did you intend to reply to the grandparent comment?