By swearing out a warrant against him, you have the opportunity to face him in court and possibly change his life. You're the good guy.
By not swearing out a warrant, you become his enabler. He'll do it again. Next time, he might not just wave, or the guy next to him might not reach for just his cel-phone. You could just as easily be saving HIS life as saving the life of an innocent who happens across his path.