Bear in mind also that until the corridor confrontation, Sincliar had no
idea that the League knew Deathwalker was there (and they didn't, until G'Kar
told them just beforehand). That makes a major difference; once they knew she
was there, he'd blow the council apart by trying to smuggle her out. If they
could get her off-station without the League knowing anything about it, THAT
was what Earth was counting on.

jms