When it comes to surveillance, the two characteristics are inseparable. That is, law enforcement /will/ abuse it while pitching the most seemingly legit cover story which is rarely the real purpose of the surveillance.

It’s always a matter of envisioning how it will be abused and working out whether it’s an acceptable evil compared to the likeliness of the legit use. IMO the answer is usually no, sadly enough. Snowden has put on display that surveillance users are in fact criminals themselves as they violate warrants and any kind of checks and balances.