If people aren't scared of negative consequences

Immediately thought of those cliffjumpers going splat on the rocky surface below.

I dunno, I half disagree and think positive and negative are essential in terms of reinforcement - that doesn't mean we can't emphasise a positive attitude towards the world generally, though.

People tend to have this assumption that humans are just born wonderful and pure and wholesome, or 'blank canvases', both of which are just objectively untrue. Humans are born literal savages. If you positively reinforce too much, they'll certainly extrapolate that in other scenarios that are closer to savage instinct. (What we see as morally abominable in a human, we just see as respectful natural behaviour in other animals, for example - but we are animals)

The fact most of us are somewhat civilised is a miracle of human history, thousands of years of training wheels and war, and as much as it sucks, we have to be taught boundaries and limitations. The second you stop, we resort straight back to savagery