It doesn't really matter if they're choosing to engage in an activity. The principle is the same. They're choosing to do something and I am choosing to stop them from doing it on no factual basis simply on my feeling of suspicion.
Also you're either severely misunderstanding me or you're exaggerating. I suggested that police can stop anyone that they deem suspicious. That obviously eliminates the notion of shits and giggles. Also one slight thing does not mean that I am proposing a police state. I'm sure you're well aware that a police state would involve a lot of other things that I'm not suggesting. Let's not leap to extremes.
It is in my opinion perfectly fair that if a police man deems somebody to be acting suspiciously, that they can seek to establish whether they're correct or not. This approach is how it's always been done. It happens here in the UK, it happens in the US, it doesn't mean a police state at all that's a huge exaggeration. Many times it's justified and it works, some times it's not and somebody is inconvenienced for all of 2 minutes. Other times, drug dealers are arrested, people with firearms are arrested etc etc.