I learned long ago not to play "try and convert me" with an atheist. Most of the time, their only purpose is to show you how they can systematically knock down every single one of your points, and then gloat that you have no proof. If someone is committed to finding fault with whatever you say, they'll always find a way to do it.
There are a couple of situations to consider:
Debating as evangelism to the lost. First, let's consider what "lost" means biblically: A person who is "lost" is one of Christ's sheep who simply isn't yet in the fold. Jesus
knows who all of His own lost sheep are. He knows each one by name. That's what enablement by the father means (John 6:44, John 6:65); that's what conviction by the Holy Spirit means (John 16:8). His lost sheep are walking around enabled to accept the gospel, and they don't even realize it. And each of His lost sheep
will respond to His voice when they hear an evangelist speaking it.
These people who are the unknowing enabled, Jesus' lost sheep, don't need debate--and certainly they don't need to debate the topics they propose. Those are only tactics by Satan given to them to prevent the evangelist from ever speaking the gospel, because Satan knows if they hear the gospel that touches the sin that the Holy Spirit is convicting them by, they
will respond to it. But as long as Satan can keep the evangelist distracted with other subjects, the lost sheep don't hear the voice of Jesus and spend that much longer outside the fold.
When we are in these online debates, we need to remember that our real target audience might be those who are merely lurking, not the person we're directly debating. Before getting wrapped around the axle, we should first think, "Wait, have I actually yet touched on the gospel itself? Let me take care of that before I go any farther."
Debating Theology with Nicene Creed Believers. This gets into the "disputable matters" that Paul talked to the Romans about. There are some matters that are indisputable--those are the elements of the Nicene (Apostle's Creed). Those are matters that are explicitly described in scripture, needing no interpretation of meaning or extrapolation of extent, having multiple explicit witnesses and no contradiction. They are indisputable, and, yes, should be defended vigorously.
There are a lot more matters that are validly disputable. They have only one witness--and maybe only a vague one at that, requiring extrapolation. They may have other verses that counter-act or limit them. Those are disputable matters, and Paul cautions us not to come to division over them.
