It's not illegal, it's against their TOS, bug difference. In any case, if there's money to be made, you'll find even more reputable entities will operate at the margins of ethics and legality. In any case, probably more cost effective to come up with a technical solution rather than suing every pop up scraper of Amazon. Or just sue the VPN provider itself?
Not sure about VPNs, but data centers usually harbor their own RBL services to blackmail you to stop doing whatever you are doing as soon as you put their network under stress or continually visit a certain domain/ip range (or get hacked and be used as a drone to DDOS some website)