Dumb players are already being punished by doing dumb things in and out of game. Their characters die more often than smart players' characters do. They screw up the plot and blurt out the wrong thing at the wrong time. They kill the helpful, friendly NPC because they are suspicious when he/she is so helpful.
In short, they make their gameplay more difficult and probably less fun for themselves and everyone else involved.
But is that enough?
Should a DM have the right/obligation to slap a dumb player?
How dumb must they be before slapping occurs?
Do they need to sign a waiver first?
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