Given sapience, beings can choose non-sapience, provided we supply them with the tools, which I think we should. The sacrifice of some measure-zero-equivalent of the population is nothing. This is a worthwhile prize to attempt.

And naturally there is no "responsibility" externally. All ethics arise from us since no other beings capable of complex cognition are present within our immediate vicinity.

Certainly one can argue for respect for all living beings and I think one should be able to construct such an example easily. My one great moral horror is that I recognize diminutive intelligence in animals that I still would gladly farm and consume. One day we will be called to task for that. My hope is to be long dead by then.