I'm in the opposite camp. Maybe I've been in the US for too long, but being told when to mourn, for how long, and how to behave rubs me the wrong way. (Ironically the instruction will come from those who normally rail against the "Nanny State").
If you want to have a national day of mourning for the funeral then have at it, but whether you are pro, anti or indifferent to the Royals, forced, extended and selective cancelations all seem a bit excessive to me. People that are going to embarrass themselves and be disrespectful will have no problem doing that before, during and after the no-sport period.
Thankfully, lack of football aside, I'll be able to avoid most of it.