Maybe "Humanity must remember each other's humanity," and start treating each other decently.

I'm afraid that only around fifty or sixty years ago, it was when there were really alien humans walking on Earth seeking to intervene actively to alleviate and improve the well-being of each other's humanity. From there, I suspect that each one boarded their own ship again to watch over us passively from some distant corner of space to observe our frank decline without being able to do anything.