Earlier quoted context omitted.
Banning (or, more precisely, disturbing operation of) a decentralized service is much easier than a big, important centralized one. You just need to obtain the DNS names or IP addresses of the nodes the same way everyone else does — by participating in the network. This way you can even selectively ban the "bad" nodes. Banning a centralized service like gmail is easier, but then you lose in productivity as 90% of you…
Your argument seems to depend on the idea that centralized services are inherently more popular than decentralized services, which isn’t necessarily true. To say that it’s “much easier” to ban hundreds of IP addresses instead of a dozen IP addresses is ridiculous. It’s no easier to get IP addresses in a distributed system than it is to get them in a centralized system. GMail is a funny example to point to, because em…
You don’t need to shut down the entire public email network (although it’s possible to do with DPI). You would only need to ban the servers that are involved in spreading of unwanted information.