Sometimes you share stuff on social media to get it out of your brain. You don't really want it to be shared around at all.
Sometimes you share stuff on social media for your friends/immediate "whatever social circle" thing. Maybe shared by some folks, but you don't want it going "viral". Esp to folks who don't have the context of the joke.
Sometimes you share stuff for the world to see. You want everyone to see and share and reshare.
It feels like it'd be cool to have a slider for this. Disabling reshares is sorta part of this I guess. Maybe there just aren't technical solutions to social problems.