It may be off topic, but reading this made me think that the ontological argument may have a similar problem to the cosmological argument. In the case of the Cosmological, when one says that God is the ground of all being, and then looks at the beings one finds in the world, one could just as easily say the cosmological argument proves some sort of devil as God. The attraction of the cosmological argument is that multiple worldviews allow for cause and effect. Thus, we have common ground to talk about First Cause. But, Christians want to talk about God as a society of divine persons with certain characteristics. And a bare first cause not only fails to prove this but opens up exact opposit conceptions of the divine nature. If we tell a nonchristian he can and should extrapolate from cause and effect, how do we limit him from making conclusions about who God is from the creation that he now witnesses?
So the ontological argument depends on the common ground that existence is superior to nonexistence. OK. But that’s an awful thin piece of common territory. Because what if I believe that no more perfect being can be conceived of than the feminine, or than a being who only does things in order to glorify himself. The reasoning of the ontological argument may say something is self-existent, but the argument seems to give permission to the unbeliever to feel free to conceive of God according to his own ideas of perfection. So again, we could end up with a Feminine or with a great glory-hound in the sky who uses others to his own ends rather than the divine Trinity.
I guess this all comes down to saying that these arguments are against atheism but aren’t so hot in dealing with idolatry.