If a state allows open carry (Wisconsin) is it okay to throw the old holster on your hip and walk down the sidewalk on mainstreet?
Probably, but I don't know much about the Wisconsin laws. I know of a person that has a photo of him taken a few weeks ago with one of this years republican presidential candidates while the person was OC'ing. Same guy has photos with other major political figures in our state as well.
Will you be arrested for ?????
Probably not, but each state varies in how/why OC is legal, and in some cities the cops are idiots and will arrest you anyway.
And if this okay, why concealed carry?
Because your employer doesn't allow OC.
Because you just don't like the (little) attention it draws.
Because you believe (incorrectly) that OC increases the likelihood you will be attacked first/for your gun.
Because you frequently visit locations that will trespass you if they know you have a firearm, but won't if they don't.
etc.... The reasons are endless and vary heavily with each individual.
As to labhound's point about someone calling the police.... In areas where OC is legal the dispatcher should be asking about the behavior of the individual with the gun. If the person reporting it says the gun is holstered and they aren't touching it, then the dispatcher should inform them that as long as the person doesn't threaten anyone it is perfectly legal for them to have the gun in a holster... This is actually one (small) reason people should OC if they are comfortable doing so, to educate the public so incidents like labhound described don't happen.
As to Tunnelrats statement... After a fairly exhaustive search of news articles from the last 30 years by a large number of people only 2 incidents of a private citizen "OC'ers" being targeted and having their firearm stolen by thugs were found. In both cases the attackers already knew the person, In one case the person was a prior victim of those attackers, and in both cases the person was known to the attackers to be unlikely to use the guns effectively in their own defense. Sorry, but that just is not a valid concern. Literally 10's of thousands of people OC every day in the US and they don't get targeted. If they don't know you they assume you are a police officer or an experienced high-end security guard or something. They won't even consider messing with you unless you look super weak, and then not even then 99.99999% of the time.
Also most thugs have no clue whether a particular gun is all that valuable or not.