This is actually the best argument against God. The argument of evil is an argument from ignorance. Is God logically coherent? That God is not coherent, is the best argument against God. But let's open a thread about that. Usually it's by saying virtues can be taken to extremes and so a more compassionate being will be less just and more just would be less compassionate, and who is to say which is better. Let's assume I won this debate and proved that virtues do have a maximum potential as far logical coherency goes.
OK, so we can assume that for any two possible beings, x and y, there is a third that is 'greater' than both.
OK, how does that prove there is one that is maximal?
Then this argument if true (God is not logically incoherent) - God would be seen to exist by ontological argument (or rather ontological argument reminds us we are seeing God).
No. We have been *dealing* with the ontological argument and the flaws inherent in how it is presented.
So, we have run through
1. The concept of 'greatest' isn't coherent if the virtues can be mutually exclusive past a certain level (they may be consistent for lower values).
2. That even if the idea of greatness could be defined, there is no reason to assume there is a greatest. For example, like the numbers.
3. You need, in particular, to show that existence is a virtue that is consiswith all the other virtues.
4. If 'balancing' of the virtues is used, you open up the possibility that a 'greatest' may not be the most for some virtues.
You are right, multiple maximum beings can't be assumed to be possible quality wise for this to work.
So you need to argue that this isn't the case, right?
So,
5. you need to show uniqueness in addition to existence.
And, just to be clear, you *still* need to show how 'seeing' or 'imagining' the existence of something can imply its actual existence.