Where open carry is permitted, I consider it to be a personal choice. It would not be my choice, but I understand that others may feel differently.
However, when someone speaks in favor of open carry, I usually ask these questions: "What do you think about the retention level ratings for duty holsters? What is the retention for your open carry holster, and how did you choose that?"
When I ask these questions, I get a lot of blank stares, and I usually have to give a brief explanation about retention levels. Occasionally, this discussion even has the desired effect of causing people to do some research before open carrying.
Note that I do not believe that everyone who open carries needs a retention holster. In some circumstances, I think it is fine to carry a Single Action .45 in a traditional western holster. But anyone who open carries should be have clear and specific answers about why they chose their carry method and their holster.