Why do we involve Internet and e-mail Service Providers?

While it is true that Internet and e-mail Service Providers, generally they are against the use of spam because it clogs their servers and bandwidth in general, many times they do not take responsability for their customers committing these crimes, and as a consequence, their IPs are blocked in black lists around the world, which affects other users who might not receive or send important e-mails because they are using a blacklisted IP address. Providers should ask to be removed from blacklists and punish customers that spam, and even suspend their service in case they do it again. If a provider does nothing to come out of blacklists, then he is considered a spam-friendly host.