Why fear things just because the eyes see them as different?

I have often wondered why people when seeing something different or what they would consider ugly.They need to either run away or kill it.When a women or a man see a spider for instance.Why do they need to kill it as if this life is less then there own.Or when they see a snake they feel they must run away .These creatures of the planet are here for a reason.And the reason is not to kill them. They were all made by the same process as being human.So if you were a traveler to distant planets would you want the being or creature from that planet just kill you.Because they thought you were ugly and some kind of threat. I myself would not feel comfortable coming down here from another planet looking like what some people have called the greys from another world.With our planes trying to shoot them down. Capture them lock them up do some kind of experimentation on.Like we do to all the insects and animals and even people down here. My thought when I have seen things that appear not from here . Is of excitement .For why would beings come down here to such a violent race of peoples.Killing each other for there different beliefs.Or because we want to have there territory. I believe that if many would open there minds to the possibility of being friends to beings outside our 8 to 5 lives we would have no problem that could not be solved for the better of all living things everywhere. But to put this in perspective I myself am also just one of the many dumb humans down here. But I kill nothing . I may not like a lot of things down here .But they are mostly the things that humans do.Not the spider the snake the bear in the woods the sharks in the water. It is more the humans that have always hurt me the most .Whether threw bad relationships bad bosses or just mean people. And I guess the question is why can't we all get along. And I mean everything. How about God bless the universe instead of limiting him from blessing all things big small and different.Peace to everyone who is willing to be peaceful to all living things.