"It occurs to me that intelligent beings, who have mastered interstellar travel, could make themselves known to the whole population of the World if they wanted to - black ops or no black ops."

Yeah, sure they could. Evidently they have not made a decision to do that on a worldwide basis. I'm not in a position to say why or why not that would be. Neither are you. There could be any number of reasons for it, most of them not particularly sinister.

"I also think it's unlikely that they would regularly crash and allow government 'spooks' to collect the wreckage."

So do I. But I don't see why it's inconceivable that they might occasionally have crashed, specially when our military has probably tried to shoot them down on more than a few occasions. Who ever said that they "regularly" crash? You just did. You just erected the straw man you are taking potshots at when you said that. How convenient for you. ;-)

"they could be in cahoots with the government"

Yeah. Heh! Some people have suggested that kind of dark theory. I don't think so. I don't buy it. But let me ask you this: When you say "they", are you assuming that there is, and has to be, only ONE lot of ETs ever visiting us? And if so, why? What would lead you to the assumption that if there are any ETs out there at all that there is only one lot that ever comes here? That would be like a Tahitian, upon meeting the first British ship to ever visit those islands, assuming that ALL other people in the world MUST be British people!

LOL! An easy assumption to make, but experience would soon prove it to be a facile one indeed. There are probably several different groups of ETs out there coming from different cultures, not just one, and they probably have a variety of different concerns and agendas, just like we do.

But I think they're more mature than we are. The reason I think so is that they would have invaded this planet and conquered us all long ago if they were the sort of immature, violent, destructive morons that we are, in a collective sense, as a culture. We are not yet responsible enough to have any business going off this planet and engaging in space exploration. We can't even treat each other decently. We're barbarians. We have not grown up yet as a species.