Soo this is a wierd topic be here is my opinion. You can have your opinion on this but this is my arguments to why they dont exist and for how they MAY exist.
1: When we Think of a typical Alien we thing of something like this: 
or this: 
So why would it be that exact? A slender figure usualy gray or green with no hair and big black Eyes. If we havent seen something and makeup what it looks like people wills start saying that it is for an example an Alien.
2: UFO's so lets get started.
''Unidentified Flying Object'' Or something like that, People Always Think of a disc shaped vtol Craft.
People also Think that they would have tractor beam that would be used to bring objects or targets up to the UFO without landing.
First of all why would it look so specific because as we hear about the aliens are suposed to be smart and inteligent right? So why would they make a vehicle of that shape because i Think that there would be more effective ways of building a vehicle.
Also why do people Think that if there is a strange light or something it is an UFO that is related to aliens? In that way if some Company made a plane with a wierd shape and i didn't know that it was a plane it would be an UFO to me or if something fell out of the sky as it would be a flying object that is unidentified.
Im sure that if some smart guy would buy a powerful light and just mount it on an ultralight Aircraft (because they are pretty small) people would say that they saw an UFO with aliens.
But lets jump over that shall we?
3: The weapons..... So people would imagine them having ray-guns but again why so specific? It could just as well have been a stick just that if they manage to make a flying object they could have something better.
4: just random stuff: I'm sure that there are living creatures around the galaxy but it could be something like a worm or spider or a new type of animal but it doesn't have to as human like that people want it to be....... There is also nothing wrong with Conspiracy theories but why would aliens take Malaysia flight 370? And why would they copme to us just to screw with us.
So i kind off rushed trough this so sorry for any Spelling errors and also the auocorrect may change some Words to have capital letters in the beginning.
Also this is not to target anyone but i just want to say what i Think why the typical aliens are false.
Extraordinary things like that maybe lived in other plannets it has a possibility to have an biological life like neptune.we all know that all living things was started in water and the energy gave by sun
If we discover alien life, it will mostly likely be Microbial life... but I hope we do discover life... but i would be scared to discover intelligent life, because we don’t know what they will do when we find them
@PorkyClown3 ok
@Minecraftpoweer No
@PorkyClown3 is he the guy wh says ''aliens'' and is kind of a meme? this guy ?
I learned from Neil Degrasse Tyson he basically said what this forum is about. :)
@InternationalAircraftCompany ok XD
No, it wasn’t me. It might have been Ethan, but I’m not sure. @Minecraftpoweer
@InternationalAircraftCompany just to be sure i looked trough your profile to see if you were the guy who made the gray Worms in sp. Basically i mean that the aliens dont necessarely have to be human like.
Hold up a second. Did you just say there could be worm-like aliens? The worm invasion is a bigger threat than we thought.
@Awsomur if we would reach other planes, then we would be aliens (or more likely, kids of those who would go to other planets) because they would be a life form from outside the Earth
Technologically advanced aliens don't need musculous bodies. They're a thing of the past in their world, especially since they have such freakingly advanced tech that their own, bodily power amounts to nothing.
However, for instance, big heads on thin necks would be impossible. A head of that size would weigh enough to bend that neck in such a way that their spinal chord would snap and break right away.
Even so, this does not mean aliens do not exist. It's just that the way we generally think of them is wrong.
Only in Independence Day. The theoretical species I just described would have every advantage over us. They’d have advanced tactics, powerful weapons, infinite knowledge of space and time and most importantly fear factor.
@Lahoski107
@Awsomur there are ways to defend against an alien invasion
@Awsomur agreed
All this being said, I don’t think aliens exist, at least not in the way we think them to. Once we advance to their level, then we’ll be able to understand what they truly are, if they are.
If there was alien life, then they would by no means attack earth in giant motherships. If they had the power to travel thousands of lightyears and reach earth, then no doubt they'd be a highly-advanced, peaceful species. They'd probably be totally integrated into their computers as well.
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As far as weapons go, they'd probably have electronic devices to disable all of our conventional weapons if the need arose.
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If aliens were indeed spying on us, we couldn't be able to tell a thing. They would no doubt have sophisticated cloaking technology that would make them invisible. Still though, they could intentionally place strange, unexplainable things on earth to see how we react. And if that were the case, then we would certainly be giving them a great response (Area 51, conspiracy theories, etc.)
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Alien "sightings" have increased since the Space Race began, and they've skyrocketed after the first astronauts landed on the moon. I think that an alien race would show much more interest in us once we finally stepped onto our moon, and even more once we reach another planet.
@Minecraftpoweer don’t quite know how to explain correctly lol
@Lahoski107 ya
When we think of aliens, we are telling them more about us than we think of them