Humanity on an evolutionary scale may rate quite high on the food chain as we know it, but to a highly evolved race capable of science we can only imagine, I would be hesitant to say that we are fully ready to make contact. The movie "The Day the Earth Stood Still" is a prime example of how an advanced entity might view us as a sub-culture. Would they accept us willingly with open arms, or would they instead feel that we posed a threat to their existence.
Another factor that could prevent contact would be the environmental differences in our worlds. Air could be like poison and our illnesses that we have over the centuries become immune to could prove to be fatal to their biology. The most simplistic bacteria like mold could act like a cancerous plague, wiping them out in a single breath.
Sure, some would openly consider an alien visitation as a wondrous event, opening unknown doors to our vast universe. Others would take the defensive posture, viewing contact as a threat, such as in: War of the Worlds, Aliens, or many other Hollywood adaptations of what could happen scenarios. I honestly believe that if we are being observed from a far off planet, than they must think we are a race of war, power, and fear.
Think how it would be perceived, if you were considering contact with a planet or civilization, and you happened to catch our broadcast signals of say; Alien versus Predator, or Signs. If this was your first understanding of a species, you might not understand the difference between entertainment and realism.
Another issue would be war itself! Could you imagine if you lived on a planet of peace, and never saw violence, and you happened to wander into the atmosphere, only to catch a glimpse of missiles, explosions, and self-destruction? Witnessing such atrocities might scare off a peaceful society; instead they might consider our warring antics as a curiosity to be observed from a distance; safe from the destructive nature.
Our imaginations and fear have become a part of our nature, and instead of living the Gene Rodenbury dream, we are bent on self-serving, and survival of the fittest. This alone may change the mind of any would-be traveler from stopping by just to say: "Hi!"
If you visit any website, or read almost any publication on UFO's, you will find both pros and cons on the side of the coin when it comes to first contact. Some even believe we ourselves are an advanced alien race that was abandoned on a planet to start over. Maybe, a war broke out between two opposing factions, and destruction was eminent, and a select few crossed millions of light years to escape, and to avoid ever being detected, they destroyed all technology that could link them back to their origins.
Personally, I feel that we have already been visited many times over the centuries. There are too many mysteries in the universe that fail to come with clear explanations; like Stonehenge, the Gaza Pyramids, and other wonders of the world that still remain a mystery.
Any person, who has ever visited a remote part of Nevada in Lincoln County, will probably already contest that our government knows much more than they lead us to believe. A small anomaly known as Dreamland, Area 51, or Dreamland, among many others is a secluded yet, well guarded secret that very few are privy to knowing what goes on. Some speculate that actual craft have been recovered, and are being used currently to enhance our own technology. Others say it is a storehouse of alien craft and bodies that have been shot down, so our government can prepare a defense to our alien invaders. Than again, it might just be a place to test new aircraft, away from prying eyes of our real enemies.
No matter what way this debate goes, the real question should not be, whether we are ready to engage in contact with UFO's. Instead the question to be pondered should be; whether the UFO's are ready to make contact with us? As humans evolve and grow at an exponential rate, we are slowly realizing that the enemy of our existence doesn't lie deep within the starry skies overhead; instead the real threat lies much closer to home!