So our heroes should refuse to help a species because said species may do bad things later? By that argument, nobody should ever be helped/rescued/saved, because we have no way of guaranteeing they will never commit evil. "Hit by a truck? Yeah, just let her lie there. Destiny might be keeping her from becoming a bank robber" is no different morally than "Planet about to be destroyed by seismic activity? Yeah, just let it blow up. Destiny might be keeping them from producing the next Khan."
I present the argument in absolute terms because that's pretty much how I see it. If you have the opportunity and the ability to save a life or a species, and no clear and compelling reason not to, then the moral choice is to save the life or the species. Could something bad happen later as a result of that choice? It's possible. We can never foresee all the results of our actions; we can only act based on what we know at the time of decision. It's equally possible that the outcome for the community or the Federation will be good, and much more likely that it will be neutral. (As most of us make no great impact on the world, most planets probably make no great impact on the Federation.) To let a person or a species die when you could save them is to assume the worst possible outcome is the only possible outcome.
I present the argument in absolute terms because that's pretty much how I see it. If you have the opportunity and the ability to save a life or a species, and no clear and compelling reason not to, then the moral choice is to save the life or the species. Could something bad happen later as a result of that choice? It's possible. We can never foresee all the results of our actions; we can only act based on what we know at the time of decision. It's equally possible that the outcome for the community or the Federation will be good, and much more likely that it will be neutral. (As most of us make no great impact on the world, most planets probably make no great impact on the Federation.) To let a person or a species die when you could save them is to assume the worst possible outcome is the only possible outcome.