What is the point of comparing Islam to Catholicism, specifically? There are plenty of Christian denominations/sects that are non-hierarchical.

Also, despite what Pope Benedict would claim, I would say that Catholicism is closer to Islam than (mainline) Protestantism is. That is because in Catholicism, the connection between the individual believer and God is limited and conditioned, since the Pope has a privileged connection with God, meaning that everyone else has a lesser connection. In Protestantism on the other hand, everyone's connection with God is absolute. In Islam, no one has any connection with God, since God is unknowable.

A bomb, H bomb, Minuteman / The names get more attractive / The decisions are made by NATO / The press call it British opinion -- The Three Johns