these sorts of rules pop in most insular cultures. its not some massive conspiracy to keep beating people, or causing them to conform. though its purpose it prolly to give the community an easy way to identify an outsider and an insider.
there are so many things within the community of jw which allow them to see at a glance who is "spiritually" "weak" and who is "strong". the community needs it to stay cohesive and to be on the lookout for danger. after all, at its core, is a group of people who want to see things in a very specific way, and for the sake of the community's preservation, it needs these rules in order to protect itself.
less insular thinking == less rules