A thought:

It seems to me that humans determine if an alien species is "friend" or "enemy" in terms of whether or not their perceived agenda coincides with the human agenda. If an alien species has its own agenda and actively pursues it, humans call it an enemy. If an alien species cooperates or allows itself to be dominated by humans, they're "good guys".

So what if you had an alien species who was right there all the way with humanity -- provides technology, scientific knowledge, ships, whatever we want we get. They give us everything we want because they realize most of us haven't got enough brainpower to rub two neurons together and even less in the way of wisdom, and those that do are overwhelmingly outnumbered by the sheeple. They give us what we want, they're "good guys"... until our own stupidity and greed kill us off. They don't have to do anything. They know we'll eventually off ourselves through our own lack of foresight and wisdom. All they've got to do is wait us out and they can just pick up the pieces. After all, what would they want with a bunch of brainless mushies? It's the real estate they want, not the bug infestation. Or, if they want to bother with us, they just allow most of us to die off, rescue the survivors, and hey, they're still good guys!

Given the toys, we'll gladly do their dirty work for them. They just waltz in whenever they want and save the day.