3) The "it's always a sin" most certainly IS a direct quote from St. Thomas (Commentary on the First Epistle of Timothy, Ch. 2).

My guess is not, since St. Thomas says the opposite in the Summa.  In any case, neither of us has been able to find the actual text.

Both St. Thomas and St. Alphonsus categorize both dress and makeup as "adornment", and only distinguish makeup in one or two ways from adornment in general, namely, with regard to the attempt to deceive men.  They say that dressing extravagently can be OK because men allow it, but makeup is wrong because men do not want to be deceived.  They are also speaking of a completely different style of makeup than the light natural-looking use of makeup that is being discussed here.  Men these days, and many husbands, not only allow their wives to wear makeup, but some even insist upon it.  So the nature of and attitudes towards makeup have changed since St. Thomas and St. Alphonsus wrote.

Listen, folks, NOTHING PURELY MATERIAL LIKE MAKEUP can ever be considered instrinsically evil.  That's the core message of St. Paul against the Jews and the Judaizers.  Everything is in the effect (does it incite to impurity) and the intent (impurity, vanity, custom, simple grooming).  So, now, to extend your principles (since both these authors classify wigs in the same class), a woman who has lost her hair (say, due to chemotherapy) now would be sinning if she wanted to wear a wig.  According to your principles, a woman who has acne or splotchy skin or bags under her eyes, etc. now sins if she wishes to cover up some of these defects with a bit of foundation and concealer.  That's ridiculous.  In fact, St. Thomas EXPLICITLY called out this use of makeup as WITHOUT SIN.  Ergo, makeup is not intrinsically evil.  From that point, there may be various non-sinful uses of makeup to varying degrees of venially sinful use, and potentially a mortally sinful use (if it's done in such a way as to tempt men against purity).

For those who claim that makeup is intrinsically sinful, you need to answer the question:  WHY is it sinful?  Strangely, neither St. Thomas nor St. Alphonsus bothered to articulate WHY it would be sinful.  How could they have missed that?  Oh, wait, they didn't.  It's because they did not consider it intrinsically sinful (otherwise they would have explained why it is).  Instead, they're always speaking in the context of motivations (vanity, custom, impurity, pleasing their husbands, maintaining their dignity and respectability, etc.).  So if they ignore any treatment of the inherent sinfulness and are always treating of the extrinisic considerations like these, then it's clear that they did not consider it intrinsically sinful.

So why would makeup be intrinsically sinful?

Because it's unnatural?  Then men shouldn't ever shave their face.  Clean-shavenness is unnatural.  We should not wear deodorant because it disguises our NATURAL aroma.  No earrings (St. Therese wore them in the picture ironically posted by the anti-makeup crowd).  No wigs for women who lost their hair from chemo or other illness.  In fact, it might even be sinful to use air refreshener to disguise the NATURAL aroma left behind after a bowel movement.  For that matter, let's all walk around naked, since that's natural as well.  We should never use unnatural medicines.  Surgery is unnatural also, so let nature just take its course.

Because it incites to vanity or causes impurity?  But it doesn't always and in all cases.  Consequently, when these conditions are absent, there's no sin in makeup.

End of story.

We're Catholics, and not Puritanical gnostic Manichaeans.

Nonsense: St Thomas clearly distinguishes between adornment and makeup (in his Commentary on Timothy, which you don’t want to take Alphonsus’s word on), when he says: “But with regard to makeup, it is always a sin...”

Let's go back to you first lie, the false allegation that all moralists unanimously agree that cosmetics are sinful.

Oh yeah: I believe someone also dug up the ever-so-authoritative.....Noldin, for you.