Mike,
I used to get really upset when accosted in much the same way and wasn't always civil about it. Now i tend to just take it n stride until pushed too far. Once I've told the person that I have my beliefs and am not interested in what they have to say, that usually ends the conversation.
If pressed beyond my limits I remove all of my clothing and start doing "The Helicopter" and in my best Scotty (from Star Trek) voice start yelling "I'm givin' it all she's got Capt'n!!!"
With few exceptions this tends to cause people to leave me alone.
Hope it works well for you too.