Originally Posted by tompe
But what you maybe need to justify is why you read books that you only like instead of reading a book you feel is really good.
Because trashy fun stuff* is fun and sometimes one just wants a piece of tasty mind candy to enjoy which may not be particularly nutritious or edifying, but provides entertainment value far beyond its otherwise perceived quality.
* Also, many now-"literature" classics such as Sherlock Holmes started out as trashy fun stuff in their creators' and the public's minds (cf. Arthur Conan Doyle's hopes that he would be remembered for his "White Company" seriously-for-serious historicals).
And many YA books are indeed of a very high quality, comparable to the best "adult"† works. The field is just subject to Sturgeon's Law like anything else.
† And speaking of "adult" works, many romance/erotica things are by the same token also as good as more mainstream-appealing "serious" literature.