We don't behave the same way towards ourselves as it was the case 200 years ago. Look at slavery, colonization, look at the environmental concerns. We ARE changing from within, we become more tolerant, less racist. Of course, there are still places where change takes more time. Clearly, the more powerful we are, the wiser we get, otherwise Mutual Assured Destruction will certainly already have occured.
A society capable of going to other stars should be able to respect the lifeforms it could encounter, if only to be able to understand it. It would certainly have the power to wipe it out of existence but why would it do it if the lifeform poses no threat? If it were a threat, it would also be wiser to communicate with it and try to reach a common understanding of what can be mutually beneficial.

Our society has reached a point where our home must be properly managed rather than wasted, because we don't have another place to live.
If we are destructive, it's suicidal and we won't reach the stars. We must first learn it here.

Raoul