I’m not sure why he has an "if" in his statement. The Bible doesn't say signs and wonders have stopped. Just like it doesn't say teaching, helps or administrations have stopped. In fact, all these gifts are mentioned alongside one another in 1 Corinthians 12:28.
As far as the rest of the claim, it sounds like simple human reasoning. God never said signs would only be done by people with perfect theology (which I doubt exist). Nor even people with “better than bad” theology.
What makes it even harder to justify such a claim is the fact that we see Paul rebuking the Galatians for being bewitched while also mentioning that God is working miracles among them (Galatians 3:1-5). Similarly, the Corinthians are commonly believed to have had many demonstrations of the gifts of the Spirit yet had to be told that no one who is prophesying could call Jesus accursed, as well as being disciplined for their pride and lack of mourning concerning sexual immorality (1Cor 12:3, 5:1-2).
Correct theology is obviously of the utmost importance but I think sometimes we separate our tendency to believe a lie, from all the other tendencies of the flesh. We shouldn’t. They’re all works of the flesh (see Galatians 5:20 which mentions “heresies”). And we are all a mixed bag working toward the higher goal to be better, and believe better.
But this doesn’t necessarily mean God won’t use us for the extraordinary.
All of that aside, I suspect that a statement like MacArthur’s may speak to a deeper ideology among many Christians. Namely, “If God were to use anybody, it would be people like me. He isn’t using me, therefore He’s not using anybody.”
Separating the Emotion from the Analysis