I thought this was interesting because if knowledge workers like journalists can do so, why not programmers, or what ever term you'd prefer to be called?
Why do we need a union in a seller's market? If I'm unhappy with my job I can quit and get a new one in a week. It's not about being a knowledge worker. Screenwriters are unionized because there are many more people who want to write than there are gigs, therefore there's a high potential for abuse.
Not everyone can do what you can do and those people in particular benefit from a union. Others have also listed why you may benefit but I wanted to make clear that you assuming everyone is like you is silly.