Then you end blocking a lot of people. Others can end up having my ip one day and i can end up having their one day...
Thats unlikely for a small block range unless you're connecting in from a cyber cafe, school or library.
No, it's not. Unless your ISP uses sticky dynamic IP, you're assigned a new IP-address
every time your modem is restarted, or when the IP expires.
Here are some IPs I've recorded lately that my network has been assigned:
188.126.89.200
109.58.31.237
188.126.85.54
Do you see a pattern? Sure, you could ban the whole 188.126.X.X range, but you'd end up banning a lot of innocent people, and there's also that 109.58.31.237 IP address... so I'd still be able to access the site without even having to use any form of proxy. And hey, if that one gets banned too, I could just restart my router!
Going around banning IP-addresses is no longer effective. It may have been 10+ years ago, but not now.