Irresponsibility.
A group of ancient aliens, evolved from mammal-like, ape-like animals, traverses the universe stopping here and there, going down to the surface without any care of how they might affect the ecosystem. In some planets they see lizard like creatures predating on mammal like furry critters, and since they find them cuter that the reptiles they scare away the predators, giving mammals an evolutionary leg up via butterfly effect.
In other planets they find ape-man like beings and they interact with them, again without a second thought to how the affect them, which is by leaving the impression of incredibly powerful beings that would affect how they chose mate in the following generations, with the individuals that resemble them, with their walking on two legs and wide foreheads, being considered the best mates.
So... Irresponsable aliens.

Irresponsibility.
A group of ancient aliens, evolved from mammal-like, ape-like animals, traverses the universe stopping here and there, going down to the surface without any care of how they might affect the ecosystem. In some planets they see lizard-like creatures predating on mammal-like furry critters, and since they find them cuter that the reptiles they scare away the predators, giving mammals an evolutionary leg up via butterfly effect.
In other planets they find ape-man like beings and they interact with them, again without a second thought to how the affect them, which is by leaving the impression of incredibly powerful beings that would affect how they chose mate in the following generations, with the individuals that resemble them, with their walking on two legs and wide foreheads, being considered the best mates.
So... Irresponsable aliens.