The fact that Minbari believe in souls does not make it so.

If a story is rigorously SF, but some of the people who inhabit the
story have belief systems, does that automatically invalidate it as SF?

I don't think it's the position of this show to state whether or not
a belief system is true but rather to explore the actions of those who
THINK it's true; not to resolve arguments, but to start arguments. (See
"Believers" for more on this one.)

What the characters believe is subjective, and is their business.
Or, as Sheridan says in a later episode, "I'm not saying what I'm saying.
I'm not saying what I'm thinking. For that matter, I'm not even THINKING
what I'm thinking."

jms