The Ontological Argument - valid or debunked?

[chimp3]

ST THOMAS AQUINAS' ARGUMENT FROM PERFECTION, GOODNESS OR VALUE, a.k.a. ONTOLOGICAL ARGUMENT (IV)
(1) We rank things as more or less perfect, or good or valuable.
(2) If this ranking is false and meaningless, then souls don't really have any more perfection than slugs.
(3) Therefore, there must be an ultimate standard of perfection for this ranking or all our value judgments are meaningless.
(4) Our value judgments are not meaningless.
(5) God is the ultimate standard of perfection.
(6) Therefore, God exists.

Could you please point me to the exact reference from which you pulled this version of the argument? I don't recall ever seeing a comparison between souls and slugs in Aquinas. The term ultimate standard of being doesn't seem very Scholastic, what translation are you using?

This is a quote from MysticKnight #207 in this thread.