You are correct about the late works, but Beethoven didn't write his 'uncorrected horrors' as a way of destroying beauty or expressing blasphemy. They had a form, they adhered to an artistic ideal which we can recognize and honor.
Some useful distinctions can be made here. Not all beauty is 'elegant', not all beauty and art is what pops into our mind when we hear the word beauty (which for me is 'Summer Glau', but never mind me!).
Frogs, elephants, spiders, mushrooms, goggle-eyed fish from the deepest parts of the sea - these have a beauty, these have a form. Grotesque beings given their form by God are beautiful. And grotesque art created by an artist in sympathy with the Creator is an honorable sub-creation: it expresses something true and beautiful about creation, its energy, its power.
But (to carry on with the example) a frog mushed into roadkill either in reality or on a canvas - this is never beauty - this is a betrayal of form, this is an attack upon form. A crushed amphibian named "Concept Frog" and displayed at the Tate would be an attack upon beauty of a sort we instantly recognize.
Now, Beethoven wrote some stuff with a difficult or ugly form. A better example for our purposes might be Browning. Every poem written by Robert Browning used a difficult or grotesque form: he used many unique meters and forms to express what he wanted to say. His poems are energetic and follow weird leaping meters, they have ugly-in-the-sense-of-grotesque-forms, in the same sense that a frog or a fish or a spider can be ugly.
But his poems aren't works of hate or evil, they are not attacks upon reality, nor do they utter frantic blasphemies.
Whereas: a counter example from one of Browning's contemporaries. The pictures of Aubrey Beardsley used as the illustrations for Morte d'Arthur are examples of evilly-inspired depictions of the human form. Beardsley's pictures have no nobility, his lords and ladies are not merely weird and alien, but they depict a betrayal of the human form. They are repellent, evil dolls.
Truly hope this is helpful.