How are you going to turn away fellow skaters from a publically owned and funded park? Ridiculous. You don't owe anybody anything more than common courtesy in this world.
In all my 20+ years of skateboarding, I've only had one really shitty experience. A high school kid who used to skate but piled out showed up all messed up and trying to start a fight. He grabbed my hair and dry humped me, I pushed him off. He walked over to the bowl. A crowd surrounded him, he threw a nearby lap dog yelling "get 'em!". The dog did not "get" anyone" He ended up beat pretty bad, blood all over his face. He exited the park to punch parked cars.