If there was any chance aliens had visited Earth, don't you think the other nations would be a little more interested in this?
Why do you think literally no one outside the US cares about this at all? — Tzeentch
Other nations do not have the resources to fund investigations into things like UFOs.
The USA does so because it thinks that they will get some sort of advantage over the rest of the world from spacer travelers, technological or military.
What I do not believe is the "fact" that aliens might be aggressive and that we need to be defended from them at any means. If they have gotten here and wanted to take over the world it is doubtful that we could do anything to stop them.
If they are peaceful, and as they have not yet attacked I think that we can consider them so, why don't they make contact? Would you talk to your new neighbor if he walked around point a shotgun at you?
Another thing that I think we need to consider is how they got here, not just the method of transport but the reason behind the journey. It takes a long time for signals from earth to reach out to the stars, so they cannot have found out about us until recently unless they were planet hoping and found us by accident.
If they are here now, we have to question how they got here so fast after receiving the signals or if they have been for a long time what were they doing before we became technologically advanced enough to be any use to them.
If they came here a long time ago to conquer us, why did they let us develop technology that would make their job harder. If they just arrived recently to conquer, why did they not stop our technological advancement? It would not take much to do so.
If they came a long time ago in peace, then it might be possible that they have helped with the advancement of the technology we have today.
So they only reason I can see for them to be here is a peaceful one, sharing knowledge.
One of the things I always laugh about in the alien invasion movies is the way they portray them as ugly monster that slobber all over everything. How could something like that even develop technology? You see them with claws trying to use the human like controls of their spaceship or weapons.
I believe that to be able to develop technology the beings must have the physical attributes necessary to be able to create and use tools. That is why ants will probably never develop an Ipad. It might take a while, but there are several other mammals that might one day actually create advanced tools.
Living environment will also play a part in advancement of any being in the universe. Dolphins are supposed to be very intelligent, but in their environment and with their physical attributes it would be extremely difficult to create tools and material to build anything.