Blocking IP addresses/ranges would be a disaster for some players if not entire ISP networks - like mine!
My ISP (Kingston Communications/Karoo) is local ISP servicing my city and some of the surrounding county and it uses dynamic IPs so my address periodically changes along with several of my RL friends/players on on here; so we could get banned accidently by havin been moved to a banned IP by our internet provider. I'm also sure we're not the only players on KC's/Karoo's network.