[computably]

> Are there examples of where we have collective decided not to pursue knowledge? Successfully?

Intrinsically, the knowledge humans choose not to pursue will not be much publicized. There's limited value in calling attention to it and it doesn't make for good entertainment. Plenty of examples provided by other comments nonetheless.

> Perhaps I'm horribly naive, perhaps I just see the SciFi future I've spent my life reading and dreaming about on the horizon and I'm blinded by the reality, perhaps my ideals around "knowledge deserves to be free/accessible" are misguided. I don't know.

I don't personally think there's intrinsic benefit in disseminating arbitrary knowledge. There's quite some difference between the printing press and nukes.