This is part VII of the Aquinasblog Dialog that was started here.
I just found this site regarding St. Aquinas' logic on woman ordination in Summa Theologica: http://www.sacred-texts.com/chr/aquinas/summa/sum584.htm (I suggest doing a text search with "woman").
Summa Theologica was written in the 12 hundreds. I'd say at least about 800 years is a long time for debate.
I'd thought you'd be interested in the Angelic Doctor's thoughts since he is your blog's namesake.
Here's what Aquinas says: "Accordingly, since it is not possible in the female sex to signify eminence of degree, for a woman is in the state of subjection, it follows that she cannot receive the sacrament of Order."
He ties the reason precisely to the fact that a woman is in the state of subjection. That has changed, especially in the past 50 years. That is exactly the reason the question should be debated; women are no longer seen as being in the state of subjection.
[More to come ...]