I do have to ask, "Is God a neighbor according to the definition of the social gospel?" In other words, if being a neighbor is giving to those in need, regardless of whether they are haters of God and separated from the covenant, then is God a neighbor when He punishes people? Is He loving them as He loves Himself?
The Neo-Marcionites would surely agree that God is not a neighbor in the OT. They would just argue that the God of the New Testament, at least in the parts they like, becomes a neighbor. The problem with that is that judgment of the wicked is not lessened, but intensified in the New Testament. God doesn't just kill people and burn their cities to the ground. He doesn't just kill their livelihood and livestock. He doesn't just kill their children. He sends them off to an eternal punishment.
But even the Old Testament God is not a neighbor according to the definition often given to the word. Not only would we have to conclude that God would not help a Canaanite who was injured, we would have to conclude that God was the One who sent the ones to injure him.
This is one of the many theological absurdities of this false claim that everyone is a neighbor or that God wants us to be the neighbor of everyone. So God wants us to be better than He is? God wants us to do what He does not do? And He wants us to do it because it's loving? Is God not loving?
Again, if we understand that neighbor refers to the covenant member, then we see that God in the OT, and Jesus in the New, is calling us to love as He loves. In other words, He is calling us to love His covenant people as He loves them. He is calling us, not to be unlike Him, but to be like Him.
John makes this clear when He quotes Christ as interpreting the command as, "Love one another as I have loved you." The "one another" are other believers. Christ gave Himself up for His people, He sacrifices all things for them. Hence, He calls His true followers to do as He does. He does not call them to do what He does not.
Instead, the love we have for unbelievers is to call them into the kingdom through the Gospel. We don't communicate to them that they are already kind of kingdom people by virtue of their having access to kingdom resources that are reserved for His people alone. Christ does not give them this and neither are we to do so.
Any claim that it is selfish not to share these things with unbelievers is simply a rebellious man's claim that God is selfish. But the road of selfishness and cruelty is evidenced by the destination to where the road leads. If I contribute toward the damnation of an unbeliever by communicating to him a false acceptance by God that he does not have, and I use those resources that could have shown love to believers in Christ in need, but now cannot, simply because I desire to feel better about my goodness and work for Jesus, then it is I who am selfish and cruel. It really depends upon what you think the end game is.
In any case, God/Jesus is in no way a loving neighbor, and therefore, does not fulfill His own law, if neighbor is understood as modern interpreters understand it.