We are not alone
The Truth is out there.
The Spaceport Crew Members fall into two categories: those who know that aliens exist and those who don't. Visitors from off world can determine which way an individual believes by looking for a small green stripe on the lower edge of these badges. Those with a gold corner on top of the green stripe are actually not from Earth. Those with red stripes should be considered exoskeptics and treated accordingly.
Extra-terrestrial visitors are encouraged to check the badges of anyone they encounter before revealing their offworld origins.
If aliens were ever proven to exist, there would be mass panic.
Humans have a tendancy to panic or become catatonic upon encountering proof that aliens exist. Galactic Alliance authorities have placed Earth under interdiction until their culture can come to grips with their place in the universe. Until then, anyone breaking the interdiction will be subject to proscecution by the authorities. Of course, there have been many infractions due to Earth's distance from any semblance of law.
Regardless of how unlikely the consequences may be, all visitors are reminded that while human reactions to aliens are hilarious, it is illegal to torment the natives. Besides, it is just poor form to take advantage of lesser beings in this way. Behave yourselves and show them how polite society interacts. Eventually with enough good examples, the humans will be ready to believe aliens are not all out to destroy them.
Vibrant and varied life exists throughout the universe. Humanity is only a tiny speck in that vastness.
In general, humans do not believe that aliens exist. Those who do are considered insane, so those who believe generally keep quiet.
While this belief has nothing to do with religion, some people consider it to be heretical, unwilling to consider this greater universe view.