{original post had no questions}

"At the end of A Sky Full of Stars which aired tonight, a Minbari
tells Delenn Sinclair must be killed if he remembers the encounter.
One of my friends considers this the greatest gaffe in the series."

Here's the reasoning on this.

First, understand that Minbari believe in reincarnation.

Second, as noted in ItB, if the Sinclair/Valen/soul issue got
out, it would likely tear Minbari society apart. The repercussions
would be devastating on every possible level, if it came before they
could be prepared properly.

In light of that, with or without a Minbari (or Valen's) soul,
better to sacrifice Sinclair (who will be reborn anyway, and maybe next
time in a proper Minbari body) than see Minbar damaged. Remember, they
don't know about the time loop, they see it as a straight-line
progression.

jms