In the current political climate you might have to wait no longer than about a decade for that to happen. Several countries already started out-sourcing prison guards and/or other security relevant jobs to companies like G4S
Do you think law enforcement aren't included in there customers? I know for a fact in the UK at least that they are.
As for being arrested by a corporation - that will change. The UK government for one are beginning a process of outsourcing some elements of front line policing.
Interesting thought, I can imagine an ad campaign on Facebook targeting marijuana growers, and then the government using the profile information of those that click through to investigate them.
This is less targeted - simply using the usage information many large commercial organisations are gathering, the stuff people are giving up without thinking.
At present it's anonymised and is being used for broad profiling of areas, but I can see that changing over time.
