Universal Grammar Theory

I read Rod Ellis's article "Appraising second language acquisition theory in relation to language pedagogy" and found it interesting, yet it left me with questions. Ellis begins by giving an overview of Universal Grammar. He calls it "an innate knowledge of grammar that guides...in the acquisition of the grammar of a particular language." Ellis critiques it as a theory based on a number of categories that should determine a solid theory. UG does pretty well in a few categories, but Ellis thinks there are still a lot of flaws. Despite its weaknesses, Ellis says that it does not compare horribly to other theories of second language acquisition. He moves on then to talk about how UG is not applicable in the classroom and just because something is a popular theory does not mean it translates to pedagogy.
After reading this article, I began to wonder what the point of theory is for teachers then. Ellis seems to say even if the theory is good it should be thrown out of the classroom if it is not applicable. That's great, but what happens when a theory is applicable, but does horribly on the theory critique scale? Ellis gives a few examples of this. Should we still use it? Isn't there a possibility of that resulting in hurting our students? This article really made me think about the purpose of theory. If we cannot apply theory to our classroom or our lives, what is it for? Is it simply so scholars can pet their egos with writing full of complexly abstract concepts and language that the layperson cannot understand? I want to know how theories move academia and pedagogy forward. Are theories important?