I'm really surprised you have an emotional reaction to someone else wearing a St. Christopher medal, minimus!
If you don't believe they have magic or powers, why are you sad if people wear jewelry, sprinkle water on themselves, etc.?
There's a lot of things we can point to that are harmful about religions; medals and holy water aren't among them. IMHO.
I guess I don't understand why the question about worship of images is brought up. Again, zzzZZZzzz. Doesn't matter.
It's against the Bible? So are a lot of things that other Bible-based religious people do. Worshipping a statue is harmless, why focus on that of all things?