It seems logical that the more advanced a civilization is, the more likely it is to be benevolent; this is a bit of an assumption, but they survived themselves, didn’t they?
Based on the assumption a war on their planet with advanced weapons would annihilate them.
After all, If you can do interstellar travel, why not fight on another planet, or just destroy it so no-one wins.
Or if there is no fighting and warriors get bored, they just invade another planet.
If there are aliens among us (mutants there are ), they have just arrived with a hiperdrive and will get active in a few days.
Or they have been here for a long time (sub-light travel -> take your time) and are working to make the earth an ‘asset’. Whether in trade, for resources or for technology or culture.
After all, I assume, different species have a different perception and evolution. Letting us do all the work is easier. (read: Let the Humans do all the probing ).