Berkeley's argument for the existence of God

[Angrboda]

So, what do you think, where is the fallacy in the George Berkeley's argument for the existence of God?
For those who don't know, it goes somewhat like this. There are things for which obviously "esse est percipii", that is, they exist only because they are being perceived by somebody. Light, for instance, exists only because it's being perceived, because, if it weren't perceived, it wouldn't by light by definition (a natural agent that enables vision). Since perceptions are ideas, they have to be caused by other ideas. Ideas have nothing in common with material things (they don't occupy space or have mass), and therefore they can't be caused by material things. Since perceptions, which are ideas, can be caused by the natural agents such as light, it has to be that those natural agents are also immaterial. Now, here is the important part: if those natural agents are being caused or affected by something, that is, the things we perceive as material, it has to be that those things that affect them are also immaterial. If they were truly material, they couldn't affect the ideas through which we perceive them (such as light), and therefore they couldn't be perceived at all. Therefore, the material world has to be an illusion. All we can actually perceive are ideas.
Now, if those things are ideas, how it is that, if we open our eyes in the middle of the day, we can't choose what we will see or whether we will see anything? It has to be that those ideas aren't ours, but that those are actually ideas of a supreme being, and that we are also one of his ideas. That being is called God.
It actually sounds smart. The argument for the material world being an illusion is quite convincing, isn't it? I'd like to hear your thoughts.

This is actually two arguments. The first being primarily an argument for monism, under the assumption that substances must have something in common with each other to interact. He oversteps, however, in calling this one type of stuff immaterial. It's like the existence of dark matter, which we know about because it weakly interacts with gravity. If dark matter didn't interact with gravity, we would have no way of knowing about its existence. But it would be silly to then posit that one type of matter is material and the other immaterial. You would simply have stuff #1 and stuff #2. Berkeley simply assumes that the substance of thought is in some sense 'immaterial'. If we had several thousand substances, none of which interacted with the other, we would run out of categories relatively quickly.