Does Materialism Need an External Agent?

I posted yesterday on the question of whether idealism requires an external agent, a claim made by the philosopher Stathis Psillos. The discussion on Twitter continued today. His comments didn’t get threaded correctly, but he asserted here that it is “well known” that idealism requires a God external to reality:

As mentioned previously, I dispute this idea that idealism requires God, let alone that this is “well known.” In our exchanges, he repeatedly cites George Berkeley and John Foster, and indeed, there is a long history of Christian idealism. So if he is primarily reading the Christian Idealists, it is perhaps not surprising that he associates idealism with theism. But it is not a necessary move from idealism to an external God.

Let me put it this way: since idealism posits that reality is mental, why is there a need for another layer of mentality outside the system (an external agent, i.e. God) to ensure structure and consistency? And would this external agent also need an external-external-agent to ensure structure and consistency? And so on. There is no need for the redundancy.

In contrast, materialism says that reality is not mental, so it is vulnerable to potentially needing an agent outside of the system who ensures regularity, structure, and the conditions for life. In other words, the fine-tuning argument. While the fine-tuning argument isn’t a knock-down argument for theism, it is a good argument — perhaps the best one that theists have. On that note, I highly recommend the discussion between physicists Sean Carroll and Luke Barnes on the Unbelievable podcast.

So I reiterate my point that idealism doesn’t require an external agent any more than materialism does, and possibly less so. Of course, if you are an idealist who believes that reality is fundamentally conscious or mental, and you want to call that God, then idealism by definition would imply theism.