To hardcore non believers in UFOs or that alien lifeforms could exist would be considered completely impossible, this question would be completely ridiculous. If the aliens don't exist, how could they possibly live among us (or may in the future).
No matter how it has come that you do believe in ETs. Statistical data of stars, galaxies, books you have read, shows you watch, unexplained mysteries, or a personal (as well as second hand experiences of UfO sighting) point to the strong possibility that there is life out there. The question isn't really are they out there.
Here are some others. Have they been here in the past? Are they on the ground or just flying the UfO's?
If they are on the ground, they would probably be somewhere around us. This would make it much easier to study the humans and their behavior. It is no accident that the first recorded sightings where in rural areas where people were scarce. If you were going to study a new species of semi-intelligent animals, would you go straight to the hive or would you try and gather information from the fringes first to get an idea of what the animals where like?
There are many theories out there that state many different ideas about alien interventions. Some state that aliens actually look like humans due to DNA manipulation. Since this is a science that is based on theories, any of them could be true.
Some things do seem to be true. Sightings have been on the rise. This could be due to the fact that information is shared more freely than any other time in history. It could also mean that the UFO's are in fact showing up more and more.
One of the biggest ideas that has to do with alien integration into human society is based on the little gray man that was supposed to have been recovered from Roswell. Like many things, mainstream media will use all of it's power to desensitize the general public to any situation that may cause panic. If you find this hard to believe, think about what the difference would be if aliens showed up today versus 50 years ago. We have actually gotten used to the fact that there are little gray men that are flying UFO's.
One thing to keep in mind is the fact that we are not at all careful with our information. All the television and radio signals that we use to communicate across the globe, continue on into space. It would be very easy for any kind of life form to just sit back, listen, watch and learn all about the human race. At the same time, we have legends, and accounts that are usually dismissed as the talk of crazy people.
Between Hollywood and the small bits of information that are released by various governments we are slowly being introduced to alien life forms.
This is one of the primary ways that aliens would be integrated into our society. As we become more and more “use” to the idea of the aliens, if and when, they decide to show themselves to the citizens of the world, we would have already gotten use to them (to some extent).
Will it ever happen? That is the proverbial million dollar question. Just in case it does, more than likely they will be more advanced than we are (since they have the ability of interstellar travel). It would be in our best interest to try to be allies and not immediately attack, which is what humans are best known for.
This could be the very reason that we have been trickled more and more information about aliens over the last several decades. Hopefully if it does happen, we can get along, learn from them and be able to integrate them into our society as fellow citizens of the galaxy.