If I want to be a writer, would I have to go to gradaute school?

I am an undergraduate student right now, and by the time I graduate, I would have received 2 BA's (History and Psychology, with a minor in Communications). Would it be beneficial for me to spend another 2-4 years in grad school and spend probably another $80,000 on my education, or should I just go enter the working world right after graduation and try to see if I can actually get a writing job?