The first of my reasons as to why you should major in writing (noting that they are not in any particular order) is that you will meet other people who share your dreams, ambitions, and fears. It is true that you will find a lot of writing major haters on Google and Yahoo Answers, and you are bound to meet a few bio-chem majors with a serious narcissism problem, but they will be far and few compared to the many people you will meet in your writing classes.
As a writing major you will always have a few people willing to read your work and give feedback, provided you are willing to return the favor, and who will actually be interested in what you've written or are working on. You will meet people with whom you can spend lunch arguing about the ending of this book or that one, who will introduce you to new authors and give you new perspective on old favorites. You will never be short of people who will happily wander Barnes and Noble with you for hours on a lazy afternoon or who will tell you they really shouldn't go because they will spend far too much money if they do.
The best thing about the people you meet as a writing major is that they share and respect your dreams of being a writer. They understand why, in a science dominated society, you could not help but choose to be a writer, despite everyone who ever told you that you shouldn't or that you would be wasting your time. They understand the feeling of finishing an amazing book and hoping that one day you might write something that left someone feeling the same way. They understand why you could not simply leave writing as a hobby and major in something supposedly more practical. Because the best thing about the people you meet as a writing major is that they all made the same difficult choice that you did; they took the plunge to follow their dreams and declare writing as their major.