>Because the systems become unusable for everyone.
In this case there is no spam or resource exhaustion going on in this case. People are visiting a forum, posting things, and viewing text / images / video files posted by other users.
What makes things unusable is when you want to follow links on the web you need to use VPNs in order to route your traffic through the correct ISPs that will properly route your traffic. There could be a future where different T1 ISPs block different sites so there is no way to browse the entire internet using a single ISP, but instead you have to cleverly pick a different ISP for each destination IP to get it properly routed.
In this case there is no spam or resource exhaustion going on in this case. People are visiting a forum, posting things, and viewing text / images / video files posted by other users.
What makes things unusable is when you want to follow links on the web you need to use VPNs in order to route your traffic through the correct ISPs that will properly route your traffic. There could be a future where different T1 ISPs block different sites so there is no way to browse the entire internet using a single ISP, but instead you have to cleverly pick a different ISP for each destination IP to get it properly routed.