This is really a pretty interesting subject, and I've really enjoyed reading everyone's responses. Let me first start out saying that I completely agree with many of you that organized religion is the cause of a majority of the worlds problems.
That being said Christianity is not about religion; it is about a relationship with God. It is trusting in Jesus and what He did on the cross for you (1 Corinthians 15:1-4), not on what you can do for yourself (Ephesians 2:8-9). Christianity is about truly accepting Jesus as your Lord and Savior.
Jesus said that He alone was the way to the Father (John 14:6), that He alone revealed the Father (Matt. 11:27; Luke 10:22). Christians do not go around saying Christianity is the only way because they are arrogant, stupid or judgmental. They do so because, based on the evidence, they believe what Jesus said. Christians believe in Jesus, who claimed to be God (John 8:58; Exodus 3:14), who forgave sins (Mark 2:5; Luke 5:20; 7:48), and who rose from the dead (Luke 24:24-29; John 2:19). Jesus said that He was the only way. Jesus is unique. He was either telling the truth, He was crazy, or He was a liar. But since everyone agrees that Jesus was a “good man,” how then could He be both good and crazy, or good and a liar? He must have been telling the truth. He is the only way.
Christianity is not based upon evidence...but it is backed by evidence. Obviously anyone could “claim” to be God. The difference with Jesus is that His life completely backed those claims.
"Salvation is found in no one else, for there is no other name under heaven given to men by which we must be saved." Acts 4:12
"Jesus answered, 'I am the way and the truth and the life. No one comes to the Father except through me.'" John 14:6