Hmm. I don't recall neutral planets mentioned in "Journey to Babel," but it's been a very long time since I watched it. I would point out, though, that much of TOS featured the Federation and Klingon Empire vying for influence on neutral planets -- the UFP trying to secure dilithium rights in the Tellun system away from the Klingons by helping with the arranged marriage between Elaan and the Troyian leader, for instance, in "Elaan of Troyius," or Kirk and the Klingons each introducing advanced technology to pre-warp cultures in "A Private Little War." The implication seemed to be that the UFP and KE were using neutral worlds as proxies in their conflicts with one-another, akin to the US and USSR doing the same during the Cold War.
