The world seems divided into those who desperately have to believe in aliens and those who desperately have to disbelieve in them.
Consider, for example, the case of the doctored Saturn moon picture
Clearly the image has been tampered with. On the one side, it is claimed that this occurred due to enhancement related to the merging of three images. On the other hand, it is used as 'proof' that something was removed which we are not meant to see.
While secretive tampering goes on, there will be fuel for the fire that makes the smoke. Such actions breed conspiracy theories. Which explanation is the true one, I don't know. But I do know that this sort of behaviour on the part of organisations such as NASA only serve to undermine their credibility.
Then, there was the case of the Air Force vs the Flying Saucers story that came out recently. A collection of high ranking officials with plenty to lose openly admitted that there had been cover-ups. They did not report encounters with bug-eyed monsters or dribbling jaw crunching aliens - just that they had been ordered to keep quiet about a set of circumstances which, at the least, strongly suggests extra-terrestrial involvement. It would have been better if they had admitted initially that unexplained lights appear to have influenced their equipment. IF there was an earthly explanation, then it might have subsequently emerged. The way it is, however, one can only wonder.
Personally, I don't doubt the existence of alien life. Whether or not it has visited, I don't know. But you only have to do the sums to realize that there are an awful lot of planets out there and the odds are than some of them are inhabited.
The biggest question, for me, is whether or not they have been here. The constant collaborative efforts of governments to ridicule the idea suggests that they have. And of course, if you look back at some of the 'photographs' of the past - i.e. paintings - then these are rather suggestive .....
The above all make those cave drawings (that 'could' be alien spacemen) look rather unconvincing even though in themselves, such ancient drawings do exhibit similarities to modern space travelers from Earth.....