There is a case to be made about some kinks; someone with a humiliation kink (often exercised by being led around on a leash) is getting close to the line (if not crossing it) of non-consensually involving others in their scene.

Though I agree with you that just "wearing a leather harness" is a pretty innocuous, and in general people don't require consent for their wardrobes in public. And on top of that, going to pride and then complaining about other attendees is at best a bit silly and at worst completely missing the point.