One of my favourite old testament stories is about society's rejects who came to David and were received by him as a company. What a lot of gospel material there."And every one that was in distress, and every one that was in debt, and every one that was discontented, gathered themselves unto him; and he became a captain over them: and there were with him about four hundred men." 1 Samuel 22:2 KJV
Plus there is always the debt each believer has to be a light in this dark world. Where should we have been if someone somewhere had not proclaimed the gospel to us. It is when the light shines brightly that many souls are saved. Witness the effect of the Reformation, which set free multitudes into the light of Christ.