I don’t know. I don’t think they should. Perhaps they don’t like confrontation in general, a common thing nowadays. Especially if you put them on the spot, or if you “challenge” the beliefs somewhere where it’s not expected. Like, if you were to go up and make some scene after Church, that’s not at all good manners. Or if it’s a group that is supposed to be supportive, then that’s also not good.
Of if someone just died or something and you say something rude.
Also, people may get angry if you offend God, for a similar reason you’d get angry if someone offended your family members or friends.