This is what I'm hearing: that which is beautiful is so because it is beautiful.

In a certain sense you could say this. For example, I find it difficult to "argue" to those who consider that Mother Teresa's work was not good, noble, and worthwhile. The fact that some people do disagree about this - and that it is difficult to argue otherwise - does not mean that the goodness of her work is just a matter of opinion.

Still, for what it's worth, St. Thomas (and others) had something to say about beauty which was not just a tautology.