I don't go around telling people that they are going to Hell if they don't become Mormons, and I don't even believe that, but I do believe that my church is the 1 true church on the Earth. I'm sorry if that offends you, but your reaction has no bearing on my belief system. As a simplistic example: If it were to offend you that I believed that 2+2 = 4 because you believed it equalled 5, it wouldn't change the fact that 2+2 actually does = 4.
I have been on a mission to Peru, and talked mostly with Catholics, although there are quite a few Protestants, JW's, Seventh Day Adventists, etc that I talked to as well. I never once told anyone that they were going to Hell, but I did believe that they needed to hear my message. They could accept it or reject it if they wanted to, but I shared it with anyone that I could.