Originally Posted by JoshJ

Except for the fact that the only reason the argument supposes god in the first place is the assumption that "Everything must have a cause", which leads to the problem of turtles all the way down.

Richard Dawkins's The God Delusion has an excellent refutation of the ontological argument.

1 The creation of the world is the most marvellous achievement
imaginable.
2 The merit of an achievement is the product of (a) its intrinsic
quality, and (b) the ability of its creator.
3 The greater the disability (or handicap) of the creator, the more
impressive the achievement.
4 The most formidable handicap for a creator would be nonexistence.
5 Therefore if we suppose that the universe is the product of an
existent creator we can conceive a greater being - namely, one
who created everything while not existing.
6 An existing God therefore would not be a being greater than
which a greater cannot be conceived because an even more formidable and incredible creator would be a God which did not
exist.
Ergo:
7 God does not exist.