"You are in danger of going to Hell." Does that statement offend you?
How would this conversation make you feel? Certainly, you would be upset, and perhaps even offended. You were not planning to be diagnosed, you had thought that you were in perfect health, and the doctor may have been somewhat insensitive and abrupt. Also, you would not necessarily take the random oncologist- a stranger- at his word. You may want to do some more research. But if it turns out that the doctor was correct, then wouldn't your attitude change? Failing to follow up on this diagnosis could be extremely dangerous. Even if it turns out that the oncologist was wrong, you would hopefully not remain offended and upset toward that particular doctor; certainly, you would not turn bitter toward all oncologists: the random oncologist that you met saw apparent symptoms, he was genuinely concerned, and he didn't make any money from the conversation.
I present the above scenario in order to illustrate how people sometimes react to evangelists. The evangelist speaks to a non-Christian, seeks to diagnose the non-Christian's spiritual condition, and then presents the non-Christian with the idea that repentance from sin and trust in Jesus Christ are necessary if one is to escape Hell and gain a right relationship with God. Hearing this, the non-Christian is sometimes upset and offended. The non-Christian was not planning to be spiritually diagnosed, he thinks he is already in perfect health, and the evangelist is often (at least perceived to be) insensitive and abrupt.
When the non-Christian is offended and upset, it is often hard for the evangelist to understand. Evangelists are used to thinking about spiritual things and having spiritual discussions. As someone who has engaged in evangelism, I can say that if a devout Muslim tells me that I am going to Hell if I do not reject the doctrine of the Trinity, I am neither offended nor upset. I think that the Muslim is wrong, and hope to talk with him about why I believe as I do, but I understand where the Muslim is coming from.
The point is, society works best when every group of believers (or professing non-believers) seeks to understand where other groups are coming from. This is NOT to say that the various groups should neglect speaking from their point of view; instead, let us each vigorously contend for our beliefs (or non-beliefs), but without personal offense or rancor.