Many of us dismiss the ontological argument as demonstrably unsound by reciting Kant's famous dictum that "existence is not a predicate." Besides the context of this line being directed toward Descartes' ontological argument, which is irrelevant to any modal versions of the proof, there seems to be a certain impertinence of it with respect to other arguments for God's existence.
Take, for example, an argument I am quite fond of: the Thomistic cosmological argument (TCA). The TCA, in its most basic form, suggests that being, or existence, or actuality, is an entity in its own right. What's interesting about this is that Kant even appears to be persuaded by this line of thought at times. As he points out, one would much rather possess an existing fortune than a non-existing one. Yet, doesn't this require an ontological difference between the two?
If being is not a real entity, then it is strictly a non-entity. But, how can two things be distinct through a non-entity, e.g. nothing? To be distinct through nothing is to be identical, so it appears manifest that being is itself an entity. Given that something exists, then, it follows that being exists.
Since I have argued on multiple occasions that being itself is Pure Act, I won't repeat myself at this time. Nevertheless, it's worth considering that we ought to be cautious when citing Kant's dictum. Besides the skeptic's interpretation, we have two additional alternatives: a) Kant was wrong; or b) Kant is being misinterpreted. I'm inclined to accept the latter.