I don't even think it's all that we're trained to be polite, so much as we've witnessed too many people being punished for their good deeds. We live in a society that is sue happy, and people sue other people for doing something kind (like exposing their breasts while the rescuer performed CPR, or breaking a rib during the same life saving act). It's all ludicrous, but it's the life we lead now because our legal system is so screwed up. It's a legal system that allows people to freely falsely accuse men of rape without any real consequence, so now when our real victims come forward, people are immediately suspicious. It's a sad state of affairs all around.