You really haven’t thought this through.
First. In order to cover the immense distances involved you have to be able to travel beyond the Einstein limits. This means drive systems that are theoretical on Earth, are real outside of a Hollywood Soundstage.
The amount of power needed to do that is beyond our imagination. Let’s use the Kardashev Scale.
en.m.wikipedia.org
Put simply. You score a Zero when your civilization learns to tame fire. You score a 1 when your civilization learns to harness the power potential of an entire planet. You score a 2 when you learn to harness the total power potential of a Star.
Just to travel faster than light you have to be perilously close to a 2 on the scale.
But let’s say that it is merely a 1.5 on that scale. We aren’t close to a 1 right now. The equivalent would be the modern military involved at the battle of Thermopylae. I’m talking Bombers, Attack Jets, and helicopters. I’m talking precision munitions with long range artillery. It wouldn’t be a battle. It would be a massacre. The other side wouldn’t stand a chance of survival, much less victory.
Now before they got to exploring our dinky little star, those drive systems would be commonplace. So two kids joyriding in Daddy’s Mercedes would have more than enough power to conquer our entire planet. They would show up and announce they owned us. Just as the European Explorers showed up with ships, firearms, and cannon, to declare that around the world.
What could we do? Our weapons would be pop guns by comparison to the power they would wield. If they reported back, it would be. Hey these guys are crunchy and taste good with Catsup. Oh and they bring their own Catsup.
Counting on this advanced civilization being altruistic is wishful thinking. Delusional wishful thinking that doesn’t recognize the battle that is waged in nature every day, by every species.