I know this thread is rather old, but in the event that someone runs across it, I would like to add that you can disable port 6000 by editing the /etc/X11R6/bin/startx file
Find the line that says serverargs=""
and replace it with serverargs="-nolisten tcp"
This makes it so when you execute startx by itself without any options, it does not start the tcp server.
Hope this helps someone