Why Humans are scared of Aliens

There are many people who say that they have seen many things like the humans but are small and the in size and do not seem to look like many humans do can these be aliens the creatures living on a different planet who may come to planet earth to either explore the same or may be even try to find a way to capture the same. There are many strange events which do not have any type of information left behind for the strangeness which is present there. For example: in a particular region on the planet once there has been a case wherein there were five men on a small motor boat and they had been fishing with all the tools one of these men had a radio which was active and these men were a part of a team of a crew and they were travelling however they were in a middle of a conversation over the radio when the radio started to get static even though in that region there is no satellite signal or any other signal to interrupt but the most amusing part is that the last conversation received from the motor boat was “I have never seen anything like this before” the ship sent another team of five in a different motor boat to check why there was no response to the radio signals sent by them only to know that everything on the motorboat was there even the radio however there was no human body i.e. there was no one available from the five men and also that there was no damage to the motor boat then where did they disappear . There are many such instances which tell us that there are many possibilities that aliens are present somewhere but this may not be true there are many other ways that the men on the motor boat have may disappeared, but it may not be a sure and perfect news. This may also be a story made up by the crew on the ship but at the same time this may also be the work of the other world. Are the aliens really trying to get hold over our planet? Is one very common question asked by children who are amazed by the whole alien concept? There are many movies which show that there are many aliens that that have intruded the world and then try to destroy the same but somehow some human has always fought the way out. Now after viewing such movies the children may be either exited and wish to be like the world saver or are really scared and worried if the world may really be attacked by such kind of creatures. Aliens can in various sizes as far as movies predict however the real sizes of these creatures have not been found out yet. If all this is really true then there may also be a possible threat to the planet and how are we humans are supposed to avoid this situation?