Sharing the gospel with an interested person is one thing. Arguing and debating with them is another. Talking out an issue is good. Disagreeing and trying to understand one another is good. However, arguing about the truth is not good and neither is it necessary. The truth (Jesus) stands alone regardless of whether a heretic thinks they get the last word or not! The truth STILL stands! If I spent all my time defending what I believe, I wouldn't have time to do anything else!
If you are a Christian out doing something for Christ, expect persecution--don't be surprised when it comes. The Bible says that all that will live godly in Christ Jesus will suffer persecution. In sharing Christ on the world wide web, we get all kinds of folks coming here--"atheists", Catholics, hypocrites who call themselves Christians, Buddhists, Mormons, Satanists, etc. They all have one thing in common--they are false prophets bringing their bad news and misinformation. We are commanded not to argue with them and I've learned the hard way to obey these commandments. Striving with people will certainly eat you as doth a canker as the scripture saith. Here are just a few scriptures for your consideration:
"strive not about words to no profit, but to the subverting of the hearers" (II Timothy 2:14)
"But shun profane and vain babblings: for they will increase unto more ungodliness. And their word will eat as doth a canker..." (II Timothy 2:16-17)
"But foolish and unlearned questions avoid, knowing that they do gender strifes." (II Timothy 2:23)
"Answer not a fool according to his folly, lest thou also be like unto him.
Answer a fool according to his folly, lest he be wise in his own conceit." (Proverbs
26:4-5)--you got to use wisdom to know when to ignore a fool and when to answer a fool.