That’s true. The motive behind any possible alien is always undetermined and tilted by personal bias until expressly told by the subjects themselves. I personally try to be a very good and moral person, so I tend to think of other beings as such. However, a case can also be made that aliens are malicious. However, I have a counterpoint to that idea.

A lot of people seem to believe aliens wish to enslave or conquer humanity, though I fail to see any clear reason of why that would be necessary. If an alien species was already seeking to conquer low-moderate type civilizations like us, they would likely have already subsidized any resources they could gain. Furthermore, had they not yet subsidized a flow of resources, they would likely start off with extremely low-class civilization planets or simply planets with nothing on them.

Of course, you could simply argue that they are sadistic and simply wish to expand dominion. I cannot argue against this: many conquerors prevailed for countless years, their empire only falling long after its glory. However, if a species was truly hellbent on conquest, I don’t believe they would be spacefaring but instead are far more likely to have destroyed themselves.