Theologically, I tend to be opposed to trinitarianism, though I do find trinitarianism useful as personal meditation. Can't say that I understand this argument. Is there a particular source you have in mind?
Maybe, then, you could give a classic example of the argument, or elaborate on the argument.
If God were unity, then He'd be both the knower and the known. All knowledge requires the knower and the known to be seperate entities in some form or another. Therefore, God must be a multiplicity of persons.
Why are we thinking of God in the terms of being a person in the first place?
Because only personal entities can love, suffer, etc.
Does God really love, suffer, ect like humans do, or do we use this sort of language figuratively. Seems mighty dangerous to think of God a we think of a human being.