All of which adds up to not feeling free to poke around in the psyches of real people. Fictional characters, on the other hand, are fair game. You can stare at them, dissect them, poke and prod them, gossip about them... All utterly guilt-free! I, personally, find that completely impossible to resist, and, for *me*, that's the answer to "why characters?" I have absolutely no idea how common or unusual I am in that respect.
Well, Betty, I don't think I could put it any better myself. I would also say that I find the Blake's 7 characters a bit better to rummage in the minds of than many series; they seem more realistic than, say, the Star Trek: TNG characters. Aside from Blake's 7, B5, and Buffy, I mostly stick to written fiction for insight on mental workings.