As a writer, you have a commitment to your audience. Your duty is to guide your readers through the text with ease and clarity to your intended message. Whether or not the message is worthwhile is completely a matter of personal opinion, but the necessity of grammar is undeniable. They are tools to your craft and writing a piece with inadequate grammar is like attempting to build a car with only a hammer and a screwdriver.
I’ve never been a grammar Nazi or even considered myself “good” at grammar, but I’m not foolish enough to think we don’t need it. You must have some command of the English language in order to effectively guide your readers because it is simply a fact that linguistic communication of our society, or any society for that matter, is based in some organized structure.
Don’t get me wrong, I always appreciate, at times even admire, the awkward styles of writers that take a non-conventional approach to writing, so it’s not to say you can’t manipulate the organized structure of "traditional" literature. But you have to know what "paint" and a "paintbrush" are before you can create your masterpiece. You can’t think outside the box if you don’t know what the box is made out of.