When the first extraterrestrial life forms to ever land on the planet Earth made contact with human beings, they were looking for one thing and one thing only: a neutral safe haven in the galaxy.
The people they made contact with decided that the best course of action would be to conceal the most significant discovery in human history for the next 60 years while secretly profiting off of the aliens' vast knowledge and technology, because the people they made contact with were Americans.
"Coming in peace is all well and good, but it doesn't pay the bills."
Thus, the creation of the Men in Black, the most catastrophic blow dealt to the advancement of the human race since MTV realized that it could make millions of dollars filming a bunch of alcohol-soaked disease farms having sex with each other. The MIB are little more than shakedown artists wearing suits, acting as a totally unnecessary broker between two groups who could interact perfectly well on their own, sort of like the IRS.
Let's look at the first Men in Black movie. Agent Jay, NYPD beat cop and walking Klansman's litmus test for how a black person behaves, underwent a vigorous selection process for MIB candidacy that left absolutely no question that he was the least qualified man for the job. He is literally a failure across the board -- he shoots a little girl in the face during a training exercise and has a completely derisive disregard for authority. Yet they hire him that day, because he can run fast. Clearly, the MIB isn't quite the elite task force we are led to believe.
Usually you save jokes about shooting small children until after the first job interview.
Once he's hired, Kay tells him that the primary function of the Men in Black is to hide the truth of alien existence from the rest of the world. Kay insists that if people were to discover that aliens not only were real but also walked the streets among them, their minds simply wouldn't be able to handle the jolt. When Jay argues that people are smart enough to deal with the revelation, this is Kay's exact response:
"A person is smart. People are dumb, panicky, dangerous animals, and you know it. Fifteen hundred years ago, everybody knew the Earth was the center of the universe. Five hundred years ago, everybody knew the Earth was flat, and 15 minutes ago, you knew that people were alone on this planet. Imagine what you'll know tomorrow."
"For example, you'll know that we think equipping untrained recruits with uncontrollably destructive weapons is hysterical."
Not only does he absolutely not answer Jay's question in any way, but he dismisses two of the most major advancements of modern science. Sure, the realization that the Earth wasn't flat and that it revolved around the sun and not vice versa were troublesome discoveries for many people, but the world didn't fucking end, did it? In point of fact, those two events were huge springboards that catapulted the human race into whole new levels of thought and discovery. According to Kay's analogy, the MIB would've erased Galileo's memory and torpedoed Christopher Columbus' fleet flying upside down in a rocket-powered submarine while listening to Elvis, because people aren't smart enough to handle such dangerous thinking.
The Men in Black are single-handedly stunting human progress, and they are doing it because they hold patents on alien technology. As Kay explains, liposuction, Velcro, microwave ovens and several other appropriately wacky examples are all confiscated alien technologies that the MIB used to make millions. This is how Jay and Kay make their very comfortable living. And they use another piece of space science, the Neuralyzer, to wipe the mind of anyone who stumbles onto their enterprise. It's not enough to hide aliens from people -- the MIB actively reverse any knowledge of them.
"We tried GHB and liquor, but that felt a little ... rapier than we were comfortable with."
The MIB aren't trying to make peace or establish Earth's position in the interstellar community -- they're just sheltering aliens in exchange for protection money, and they're doing it by deliberately standing in the way of human evolution and the progress of the entire universe while Will Smith spits out some Kid's Choice Award-winning rap. How is that not a crime?