BillD, I agree with you and your read on those situations. With those who shamelessly proselytize their belief systems and who I don't know and respect I can be more direct and give them the brush off. With those I know and respect I need to explain that my beliefs are too personal and held too closely to share with anyone who doesn't also share my life.
On the use of gratuitous foul language, I find it is better if its use is limited. That way when you do find a situation that calls for that language it has a better chance of fulfilling its purpose. Remember that overuse knocks the shine off of anything. If you commonly use those words they will not shock anyone. If you are known as someone who does not normally swear then the vehemence of your anger will shine when you resort to the language of anger.