I just noticed that the ontological argument and the moral argument that theists often use are actually incompatible with one another. The ontological argument, in its modal form, states that it's possible that a maximally great being exists as its first premise. A maximally great being is described as possessing three omni-properties (all-powerful, all-knowing, all-loving). But how does one arrive at that conclusion? The proponent of the OA must assume that there exists an independent, objective metric of goodness in order to determine what maximal greatness is. This would mean that goodness cannot be grounded ontologically in god and would contradict the moral argument, otherwise the OA becomes viciously circular. Thus, the ontological and moral arguments in tandem are incompatible with one another.
To put it another way, if god is the standard of goodness by which all moral truths are measured by, then to use that same standard to measure the criterion by which we determine what a maximally great being is, it makes the ontological argument totally circular. God is being presumed in order to determine what is god is. Otherwise, how would the theist arrive at the idea that being all-loving is maximally great? And what standard would they be using to determine what an all-loving being can and cannot do? This would all have to be determined without presupposing a standard that is ontologically grounded in god, and would thus have to exist independently of god's existence.
So it appears we've got a catch-22 here with the ontological and moral arguments. I can't see how a theist can have it both ways.