One motivation for sending humans into space is as an insurance policy against a mega-catastrophe on Earth.
Often cited is the impact of a large comet or asteroid which might destroy our civilisation or even our entire species. More likely in my view is a sudden pandemic, either naturally occurring or through the accidental release of a virulent bio-warfare pathogen.
In any case, over a period of millennia, there is no lack of potentially species-annihilating hazards. If all that stood in the way of human survival were some indigenous microbes on another world, few people would have scruples about ignoring their “rights”.
If a planet had complex plant and animal life, there should be strong ethical objections to contaminating it with terrestrial organisms. Even if the two forms of life were so biochemically different that direct infection was avoided, it may still be the case that the terrestrial invaders would plunder some vital resource and deplete the indigenous ecosystem.
Earth organisms might spread like the rabbits in Australia, and elbow the indigenous life aside, driving it to extinction.
That issue would be greatly sharpened if a target planet is found to host intelligent life. In the movie Avatar, resource-hungry humans muscle in on the planet Pandora to the extreme discomfort of its indigenous population, although in the interests of Hollywood-style justice, the pesky human invaders eventually receive their comeuppance.
There is no guarantee that future generations of humans would exercise respect for the rights of alien beings, nor can we be sure that aliens would respect ours.To read more, click here.