The entire reason I made my junker nearly 2 years ago was for freedom - the ability to go anywhere, haul almost anything, make allegiances and enemies where I saw fit, be my own boss, etc. etc. I still maintain that on the same character, if I joined a faction such as the congress there would be rules, restrictions, limitations. I can do more on my own than I ever could in a faction.
Plus, a faction tag lets people know who you are from systems away, easier to sneak around when you're untagged.