You have to be exceptionally naive to believe that we are the only living beings in the entire universe. Surely the vastness of the universe that has already been clearly demonstrated by the scientific community would suggest that mathematically the probabilities of us being the only living beings in existence are remote at best. While it is difficult to believe for many people, we simply are not very unique in the grand scheme of things. The conditions that came together to form life on this planet were not as miraculous or divine as some would have us believe. A set of random and unremarkable conditions and events occurred to conjure life on Earth. The same type of events and conditions could easily occur on billions of similar planets throughout the universe.
However, the assertions made by Sergeant Stone and the other seemingly well credentialed individuals of the Disclosure Project are difficult to believe. While it is entirely plausible to think that we have been visited by other life forms at some point, it is unlikely that we have the technical means to catalog the type of data suggested by the project. It is equally difficult to believe that our government is creative enough to maintain such an Earth shattering secret for as long as it has given the fact that other important secrets that have nearly toppled presidencies have managed to leak out without much trouble. The pieces of the puzzle simply don't fit together well enough to make the assertions believable.
Despite the huge number of apparently credible witnesses and participants in the cover up that have been named by the Disclosure Project, none are officially recognized by the US Government. If such information is available why is it being trickled out in a tightly controlled limited fashion through a totally unrecognized organization instead of the President of the United States disclosing this information in a worldwide press conference? Why also are we led to believe that only the United States is the bearer of such monumental information? Given the lack of a centralized world leader, why would such information on alien species and technology be left solely in the hands of one nation?
While it is likely that we are not alone in the universe, it is also likely that what the "experts" and "witnesses" of the Disclosure Project are aiming for has more to do with self aggrandizing and personal profit then with sharing vital information with the world. The list of expert witnesses supporting the allegations of the Disclosure Project is long and seemingly impressive. However none of those listed on their website have been acknowledged by any body of standards as experts in their proclaimed fields. The impressively outfitted press conference from 2001 alleging that 57 alien species have been cataloged is certainly convincing. Then again so was the alleged Alien Autopsy video as well as so many works of creative fiction put forth by Hollywood. The appearance of legitimacy does not translate into a legitimate project.
There are many people who would like to believe that we are not alone and that there is some advanced civilization that is watching over us. Now that mankind has the ability to annihilate itself for the first time since the dawn of civilization it would be very comforting to think there is a protective guardian keeping a vigilant watch over us like a parent over a child. Clearly the human race is too immature and too primitive to responsibly wield the power that we currently have at our disposal without some higher intervention, be it divine or alien. But the truth of the matter is that we are left to our own means to survive and cannot rely on a fictitious alien presence, not yet at least.