We cant imagine "aliens" as long as there is no clue.

For the sake of argument, lets just assume that there is alien life somewhere out there in any of the 125 billion galaxies. We also assume that they are intelligent and capable of launching an invasion. We are not going to argue about a alien bacteria or nematoda, we are discussing intelligent aliens.BOP on the Con is to show that:1. Why we can predict the appearance of alien without meeting one, i.e. how they look like and why we are related to them.2. Why aliens have the reasons to invade, destroy or parasitize human kind. Con 1.Based on the origin of ourselves or any other living being on this planet, we can see some certain patterns. We have reached today's condition through thousands of millions years of evolution process. The laws of evolution, like "survival of the fittest", will be applicable everywhere in the universe. Why?Because, the laws of physics are true for any reference frame all around the universe. This is one of the two postulates of Einstein's theory of relativity. If the laws of physics hold, the laws of chemistry will hold too. That is, if Hydrogen and Oxygen produce water in the planets of our galaxy, they will produce the same in any distant galaxy because laws of chemistry are nothing but the laws of physics. So even if the environment is different, the laws of chemistry and evolution will remain the same for any part of the universe. Of course the evolution process might be different, but laws are laws, they will be same.Consider a scenario. How the elements of periodic table were predicted even if there was no clue? They were predicted based on solid patterns and facts. Patterns of the current elements which told us about that the undiscovered element should also agree with the same facts and properties. Just in the same way, based on our current understanding of the nature and the universe we can predict something. Just like predicting a black hole and dark matter even if we don't get to see them. The Higgs-Boson was predicted decades ago, remember?The aliens' look would depend on what kind of planet they evolved on. If they evolved a planet much like ours, then they are most likely to have similar features of us, like Carbon based creatures, having two arms, two legs etc. However, if they evolved in a planet different than of ours they can be silicon based or carbon-silicon based. They may inhale Nitrogen instead of Oxygen, but some features are still predictable. Because these are facts, natural laws.For example, if the aliens are intelligent, - 1. They will have to interact with the surrounding environment. Because they will need energy to survive as any life form around the universe. That means, they will have some sensory organs. And the best sensory organ for a predator are the eyes. They will have eyes. Those eyes might not be visiable light based, they might be infrared based.3. To sense three dimensional universe they need to have at least two eyes.4. They must have some kind of complex molecules to carry out bio chemical functions. Like we have proteins, glucose in ourselves. The laws of evolution will still rule, meaning these complex molecules will also evolve to best support the alien in different bio-chemical environment.5. Intelligent and capable aliens will have to have a process of movement. Which means they will have legs or tentacles just like us or if they may fly, they will have wings to help them do that in the atmosphere of their planet. On the other hand if they dwell in some liquid environment like the ocean of water or liquid Clourine or Methane, they will have fish like organs to support them that movement. Because laws of evolution works in that way.6. To survive they must take some kind of energy from the environment, extract that energy and dispose the waste. Which surely give us some hints of how they might behave.7. They will also have to process information, otherwise why would we call them intelligent? That is they will have some kind of brain or nervous system to do that.8. Also, as per evolution they will have some means of reproduction to ensure their race's survival.These are not only true for the planets of our own solar system. May be the aliens will not be chemical based, they will be energy based. But still we are not totally blind. We can predict and imagine them because we have the knowledge based on our current understanding of the universe and human imagination is infinite. You just don't get to know which one is true until you meet one of them.Con 2.As I have stated earlier, if the aliens are intelligent, they will evolve and they will need energy to survive because without energy no life being can survive. They must eat or take in something, say food and convert that into energy. A scientific truth. Now what if they run out of the energy of their planet? Just like us? Then they must look for alternative sources of energy which is the best reason for a possible alien invasion, even if they had different evolution. Because we are talking about energy here. Not food or flesh. I'm not saying aliens have to destroy us or eat us. They may come in friendly and may trade with us. Remember how East India Trading Company used to get valuable resources from the Africans luring them with simple ornaments?You said about Titan. I can guarantee you that if at some point we run out of silicone or energy, or if we direly need something from Tital, we will certainly invade Titan, even if we have to kill those aliens. Did you watch the movie "Avatar"?Science says that there must be a cause for any result. We have eyes because we need to see. The same is applicable for the aliens too. Because as I said, physics is same everywhere.Therefore, we do have the ability to imagine aliens even though we haven't met them yet.