Firstly, I agree that it's on the owner to understand a chameleon's boundaries, safety parameters, etc. It really can be a case-by-case basis. But since you asked, here's my actual opinion:
While I agree that the likelihood of this being detrimental is fairly low, I still don't think it's worth it. Your chameleon has nothing to gain from this activity. Only you do. IMO, it's selfish to do something for yourself which uses a living animal as a holiday prop, especially when you know there is even a small possibility of it causing harm. No photo opportunity is worth willingly risking an animal's wellbeing. Especially a loved one.
I see it as a simple risk vs reward scenario. The reward (a cute, if controversial, picture) is minimal and self-serving, while the risk (a harmed chameleon) is potentially severe, even if it is unlikely.