It is.. but BGP is a sort of privileged system in that once you're peering with another provider, you're trusting them to not put garbage routes out. When they do, those garbage routes propagate. The decentralized-ness is a strength as well as a weakness.

Much like IRC, also a decentralized system, where a rogue server (a server has privileged access) or services package (same) can cause widespread issues across the entire network.