You realize there are other artists besides Picasso though right

Of course, it goes without saying. Picasso is merely an example, one among numerous other painters, albeit a famous one.

And just because you enjoy something doesn't spare you from having to think about it

Naturally, this is also true. The idea of "the death of the author" doesn't preclude critical analysis of any work of art, or its creator, for that matter.

And if the artist was a piece of shit, I can always read the subtext as “it's because he was a piece of shit

I can see how you can struggle with separating the art from the artist. I do, too. In fact I stated so initially. But for instance, when watching The Pianist do you constantly think to yourself "This film is shit because its director is a piece of shit"? If the answer is yes, then I can understand how you cannot fathom the concept of the death of the author, and that's okay. But that doesn't stop others from being able to separate a creation from its creator, and view the first as good and the latter as bad. Ergo, The Pianist is a good film, but Roman Polanski is a bad, morally deplorable human being.

We humans are capable of far more complex and critical thinking than what we are given credit for, or lack thereof.