I don't think of the US Open and PGA Championship as being primarily spectator events. I think of them as national championships that happen to be of interest to spectators. To me, it makes sense to hold them with or without fans on the ground, just like it makes sense to hold our club championship - even without galleries, I like that the best players get to compete for the highest crown.
The Tour, to me, is primarily a spectator showcase. It's a Tour, after all, so the idea of playing Tour events without spectators is a little more complicated to me. But plenty of people are happy to be able to watch, and keeping fans out has seemed to do what was hoped in terms of allowing entertainment to continue without creating significant risk.
When do we think fans start returning to the grounds? Is there already a date planned, or no? A patron-less Masters would feel weird to me. Usually the lack of fans isn't weird, but when Tiger made birdie on 18 in round 1 at The Memorial and was met with silence, that was strange. Augusta without roars would be strange too.
Then again, it's Georgia - the governor may insist that twice as many badges as usual are issued.