When people say something like this, what most would take away is "oh, so I guess not much will change then...since they've already being doing that".

But it would be wrong to think like that. When the activity actually becomes legal, such actions will grow by orders of magnitude. Maybe they were already abusing their powers against many people - but if it gets legalized they will shamelessly abuse them against many more.

Indeed. Legal warantless surveillance is admissible in court, while the illegal kind is much less so. Not only will the use of surveillance grow, but so will the likely consequences of being surveilled.

But this is a good thing. It will show people that surveillance does come with consequences. Only then it might be opposed.