The job of the linguist, like that of the biologist or the botanist, is not to tell us how nature should behave, or what its creations should look like, but to describe those creations in all their messy glory and try to figure out what they can teach us about life, the world, and, especially in the case of linguistics, the workings of the human mind.
The variety of shape, pattern, and color found in the languages of the world is a testament to the wonder of nature, to the breathtaking array of possibilities that can emerge, tangled and wild, from the fertile human endowments of brain and larynx, intelligence and social skills.
Before you judge me as some kind of 'anything goes' language heathen, let me just say that I'm not against usage standards. I don't violate them when I want to sound like an educated person, for the same reason I don't wear a bikini to a funeral when I want to look like a respectful person. There are social conventions for the way we do lots of things, and it is to everyone's benefit to be familiar with them. But logic ain't got nothin' to do with it.