Aliens are not known to actually exist, so your question is unanswerable.
We have not yet made contact with any aliens.
Although there are many reports about aliens from outer space, we have no definite, confirmed contact with any such aliens, and therefore it would be impossible to say whether aliens would prove to be useful or destructive, if we actually were to encounter them. We will find out when and if we meet them.
Many do, many don't. Some fear the idea that there may be aliens. Some would look forward to meeting them.
It is said that many people have gone missing and return a week later not remembering anything. In the mid-nineteen hundreds many sightings were reported but they could have been fakes or for money. So the answer is still unknown if aliens have ever made contact with humans.
"Why wont aliens kill humans" ... Theyre afraid.
We have not yet made contact with any aliens.
'Aliens' are real. In any given country, a foreigner may be described as an Alien.
We do not know. We have not made contact with any aliens.
We do not know. We have not made contact with any aliens.
We do not know. We have not made contact with any aliens.
We have not made contact with any space aliens.
We do not know. We have not made contact with any aliens.