how about users be allowed to block facebook?

what device are you wanting to do this with? A lot of netgear routers (and other routers for the matter) support website blocking.

https://kb.netgear.com/24053/How-do-I-block-Internet-sites-on-my-NETGEAR-router-using-the-router-web-interface

plemans the "feature" referred does not work with https connections on many if not all Netgear Nighthawk consumer routers - only on plain text http. And it won't help when it comes to blocking e.g. FB access by the mobile Apps - this feature requires either a complete revision, or it should be removed as it's misleading at least.

schumaku Thanks, pulled space cadet and forgot about that. 

How about using opendns for domain blocking and pointing the router at it? 

Netgear Armor - Powerd by Bitdefender should be the answer for typical home users.

Not all devices have the option of netgear Armor. but for those that do, it'd work great.