Probable Cause is the lowest standard for an arrest. It is admittedly a very low standard, but in order to legally arrest someone, the police MUST have probable cause to believe that person committed the crime in question.<quoted text>
I think you're incorrect. Police can arrest anybody they desire. But if it's determined police had no real evidence to arrest somebody, then it becomes a liability for the city. The Duke LaCrosse case comes to mind.
After this event became a national circus, then the city decided to take the risk of arresting Zimmerman.
The police can detain someone--detaining means a Terry stop--if they reasonably suspect he has committed a crime. This is the reasonable suspicion standard. If they suspect he has a weapon, then they can search him.
Detainment does not mean moving the suspect from that location, although in the case of a DUI, the courts have allowed movement to a safer location, like a nearby rest-stop to conduct field sobriety tests.
The police cannot "arrest people for anything." Doing so would violate the suspect's Constitutional rights under the Fourth Amendment's search and seizure clause, which specifically states Probable Cause is the minimum standard for any search or seizure.
Do the police violate the Constitution? Of course. Abuses happen in all professions. But that doesn't change the legal standard.