We debate the idea of God because it is something we cannot prove or disprove with our logic and senses. Atheists believe they can disprove God with human logic, but their own closed-mindedness to anything beyond the physical dooms their proof. Anything could exist out there that we could never detect. Those of faith have the same credence, as their proof comes from personal experience, ancient texts and so-called miracles. Atheists do not believe in God because they see no proof and because belief in God limits their ability to do as they please. Believers believe because they cannot explain the universe in any other way, it provides structure and they believe that there is proof.
The reason to debate it on the modern ground is not to convert someone from one place to another (unless you're an evangelical) but to cause someone to understand "why" you believe as you do, and to help the other person to at least tolerate and hopefully accept your beliefs as valid, though there is disagreement. Also, searching for a common ground (such as "I see no proof for God, but I cannot disprove God for you, and it is possible he may exist") becomes important as our beliefs increasingly diversify.
The reason to debate it on the modern ground is not to convert someone from one place to another (unless you're an evangelical) but to cause someone to understand "why" you believe as you do, and to help the other person to at least tolerate and hopefully accept your beliefs as valid, though there is disagreement. Also, searching for a common ground (such as "I see no proof for God, but I cannot disprove God for you, and it is possible he may exist") becomes important as our beliefs increasingly diversify.