Why should scientists consider the impact their work will have on human before proceeding with any new experiment?

I would think that scientists are bound by an ethical code
of conduct to consider the impact of their work before proceeding with it.  I think of
the scientists who helped develop the atomic bomb as an example.  The standard telling
of this narrative is that they were completely zealous in the development of this device
towards many ends.  They saw it as a means to end the war, or to end war, in general, as
a source of limitless power, as well as a means to engage in a scientific impossibility
of splitting the atom.  Yet, I think that all of the scientists involved understood that
there was a need to talk, to discuss realities that would arise from their experiments
and discoveries.  Such a moment demonstrated that while science is a boon in so many
ways, it also involves a level of ethical and personal responsibility that requires
discussion and discourse before proceeding with any new
endeavor.