I am interested in seeing how many people believe (or don't) in aliens and why. A person who doesn't beleive in them might argue the following points:
1 - The universe is huge and the chances of them visiting Earth is slim
2 - If a type III civilization existed we would notice them
3 - They would have trouble communicating with us
4 - They would require resistance to the germs on Earth
Well I do believe in aliens and I will explain why, going over each of these points.
We are just taking our baby steps as a civilization and we can't assume we know the workings of a type III civilization. NASA has admitted to the existence of unidentified objects in space, some NASA footage even shows such crafts leaving the Earths atmosphere. Professionals are unable to explain such events and come to the conclusion that they are highly quantized crafts. They can get up to 3 nautical miles wide, and can travel at ridiculous speeds. NASA has endless footage of such crafts. 62 children all witnessed the landing of a UFO and the aliens that got out of the craft. The children claim the aliens were telepathically trying to warn them of something but that's getting off topic. Did 62 children lie? A man recently claimed to have been abducted by aliens, he also claims that they implanted a microchip of some sort inside him. Experts soon found the device inside him and began testing it. It was found to contain isotopes never seen before by man kind and it couldn't be cut with the doctors scapal. Has a secret quantum/particle physics department of the Government been developing such isotopes for use in microchips and implanting them in people or have aliens done it? Well unless the Government try to act like aliens in hope of keeping in the dark, I don't think it was the Government. Search up all of these occurrences if you question my credibility, they are fact.
1.
So the first question is why would they visit Earth and how likely is it? The universe is infinite, you might picture it as a sphere, expanding since the big bang. So what happens when I get to the edge of the universe, go past it and start exploring nothingness, I think that I will eventually find another universe. Time did not start with the big bang, that is the start of our universes expansion, time is infinite and I obviously can't prove that, but consider this: First we were the center of the universe, then our sun was the center of the universe, now our universe depicts the start of time...hmmm. My point is, given infinite space and time anything can occur. It is the premises of life. An infinite amount of life forms exist out there, given enough time, chances are one will discover Earth.
2.
Do you really think a type III civilization wouldn't have the technology to stay hidden. You ask why would they hide themselves? Well I'm going to give to 2 answers to this question: #1 They are observing us. #2 They realize we are not ready to become part of a galactic civilization, we are primitive, we kill each other for god's sake! Until we wise up, they are doing themselves a favor keeping hidden, but they cannot remain perfectly hidden and we now know they exist. My personal theory is that they came to Earth long ago and combined the genetics of apes and their own species, this is scientifically backed up: the missing chromosomes, the lack of a middle man remains (the stage in between primates and modern humans). I think we are their grand experiment, a genetic combination of themselves and us. So if they are so advanced, wouldn't we notice their huge infrastructure? Again I will give 3 answers: #1 They live in an entirely different universe. #2 They are able to make the infrastructure invisible, it is all highly quantized, visible only with cameras that can pick up electromagnetic frequencies out of the visible light spectrum. #3 They extract zero-point energy from the quantum foam so there is no need for massive energy harvesting machines.
3.
They would have absolutely no trouble communicating with us. They could learn all the languages of Earth in the blink of an eye using super computers, but I'm sure they already know all the languages, they have been observing us since they created us. They don't speak vocally, they talk telepathically, and can talk telepathically to humans, although we must respond vocally.
4.
There's a few ways they might achieve this: genetic manipulation of themselves, an atmospheric shield or they might just exist as higher beings, rid of a physical body and the need for physical necessities, beings made of pure quantized energy, able to change into any form they want to take, they can even look "real" and solid if they like. In natural form they might look like a ghost. This paragraph is all speculation, as is a lot of this post but you should get the point, they are much more advanced than us and not to be underestimated, we are just variables in their experiment!