I have no doubt that Judas knew it was wrong for him to betray Jesus. After all, he made his plans secretly, and afterward he tried to return the money and ended up committing suicide. What a tragic life!
Why did Judas turn against Jesus? Some have suggested that he was driven by greed; the Bible tells us that from time to time he stole money that people had given to Jesus to support His ministry (see John 12:6). Others have suggested that Judas was hoping Jesus would become a great political leader and would give him a position of great power and prestige. Once he realized that Jesus wasn't going to do this, he turned against Him.
But the deeper reason is that Judas refused to believe that Jesus was God's instrument, sent from heaven to save us from our sins. Although he had every opportunity to hear what Jesus taught and witness His miracles, in his heart Judas remained an unbeliever. Was it logical? No -- but then sin never is. When we sin, we are saying that God's promises are lies, and our way is better than His. It isn't logical -- but we still do it.
Judas' life stands as a solemn warning to us -- a warning against the dangers of hypocrisy and unbelief. Make sure you aren't like Judas, but by faith turn to Jesus Christ and commit your life to Him. The Bible warns, "How shall we escape if we ignore such a great salvation?" (Hebrews 2:3).