Well lets see. Turning around AT a checkpoint would be probable cause. Just as much as seeing a cop and turning around and going the other way. Same damn thing.
Also, once again, you DO NOT HAVE TO GO THROUGH THE CHECKPOINT. I went to my GF's house friday night. I got off 315 on Henderson road, came up Reed, went to her place on Bethel across from the Kroger. I didn't get chased, I didn't get stopped, and I made my own decision to not go through the checkpoint. You are arguing something that is false.
PLUS, U-turns are illegal in the city of Columbus, so that doesn't make ANY argument null and void as the car just committed a traffic violation.
Once again, tell me how they are forcing people to go through a checkpoint. Please.