I've got a much longer post rumbling around in my noggin, but I keep making a hash of the prose, so I'll write a short one with the same point.
Recently, we had a customer come in for food at Catholic Charities sporting a $100+ fingernail paint job. It was awesome, but clearly a stupid decision for someone in that position.
People make stupid decisions all the time. Sometimes we pay a small price, like when drink too much and end up with a hangover. Sometimes we and others pay a really big price, like when we sleep with someone we ought not and that union bears a child.
Logic doesn't do a very complete job of preventing stupidity. We're rationalizing creatures, not rational ones, hence the $100+ nail job. What feels good often trumps what makes sense, which is why we sometimes drink way more booze than we should.
If the culture doesn't dissuade you from stupid, if the culture reinforces stupid, you're going to get lots more stupid. The Victorian cliche, "That sort of thing just isn't done, old boy" in reference to illicit behavior, was the culture trying to dissuade you from stupid.
When we decided to drop objective morality and judgmental attitudes, we unleashed a whole lot of stupid.