It's necessary to provide a comprehensive service(not just TV, of course) where everyone has things they can enjoy, and can moan about the "rubbish" they don't watch.
If you want to know what we'd get without the licence fee, then look at the diminution in quality at ITV since the 80s, when Thatcher ripped up all the regulatory standards and set it free.
ITV is loads better than it ever was..