ICANN is easy to unseat: just point your computer to an alternative DNS server.
Yet it is absoutely true, all it takes is changing some settings so that computers point elsewhere. ICANN derives its "authority" from voluntary behaviour of network admins.
Examples:
• if a site is banned from ICANN DNS, then there is no other choice,
• if I want to keep bots, spammers, search systems, providers, and government out of the door,
• if I want to welcome technical elite but hide from everybody else, like it was in old Internet.
• if I don't want to pay X$ every year for every domain.
• if I want to have a cool name for my site.
• if I want to create overlays for popular sites, to fight ads, spam, promotions, PR, and unwanted content.