[bisonbison]

I think your strategy sounds fine, though if you don't find it wearying you might just choose to take everyone (even the relatively benign ones) and tell them in private.

People get angry because it's humiliating to be casually surveyed and diagnosed without permission (even though we'd all do it if we had the skill), and because the concept of cancer is terrifying, whatever it's prognosis.

But you're not giving people prohibitive advice: "hey cecil, maybe you should stay out of the noonday sun." You're giving them caution where they may have none. You're doing a scary service to them, and I think it's a good idea. If you agree that it's a good idea, you just have to make peace with the often crappy reactions.