On the 40th anniversary of the Moon Landing, a writer bemoaned Man's failure to send humans beyond Earth's orbit in the years following that historic event. Personally, I'm glad Man has remained (relatively) Earthbound. Imagine the damage that could be done if Man treats any new lifeforms he might encounter as he has treated his own and other species that reside on this planet.
No. Really imagine.
Does the planet have a resource we want? No problem. Start a war to seize it.
Does the planet have an intelligent lifeform that differs from us in some way we consider significant and dangerous? No problem. Eradicate it through genocide.
Does the planet have what we consider a non-intelligent lifeform? No problem. Feel free to use it, abuse it, kill it, or drive it to extinction.
Humans should remain Earthbound until they have learned to treat their own and other species with respect, and to value living creatures no matter their appearance or intelligence level.