I have a problem with surveillance in general and I don't think that private surveillance is really any better. Because it still descends from government, I think you'd end up with most of the same problems in addition to problems resulting from trying to make profit.
I mean, what surveillance companies are going to get the most contracts and make the most money? The ones that 'discover' dissent groups, non-peaceful demonstrations, and terrorists. Given that these are relatively rare in our society, a business has incentive to forge evidence on groups and hand them over to law enforcement. Since we're just talking surveillance, no real crimes have to be committed. We can't expect the businesses to be transparent in their methods, because that's their competitive advantage. Whatever government agency signing the checks would be just as happy with this as with their own illegal spying, because they get to point to all these 'wins'.
I guess my point is that moving a controversial issue from the public sector to the private sector doesn't make it magically better. You can say you're fine with it "as long as it's legal", but that qualifier can be applied to government surveillance, too. The problem is that this kind of surveillance lends itself to corruption. I've seen nasty things happen at Thanksgiving parades. What percentage certainty do we need of a demonstration becoming disruptive before law enforcement comes down on the heads of the organizers? 90%? 50%? How often do you think a protest against the current establishment is going to cross that threshold?