Of course. your logic is all you have to go with – but you may still recognize its weaknesses. Perceive that you do not perceive all. As we’re quoting Rambam – like his mashal of life in utero. The issues under discussion, where one may or may not want to hear another’s opinion on, are generally not two plus two. Few things are.
I don’t think your second point is correct. We cannot fathom Him, but we can know what He is not, and cannot be. We can logically understand that He must be one, in the absolute sense, infinite etc – by understanding logically that it could not be different, even if we don’t understand what He IS. RAMCHAL deals at length – we define Him by what He is not. Therefore something which would contradict that – i.e. imply that He is something He cannot be – is a logical contradiction.
Charlie – could you elaborate, or give source ?