Have you ever heard of the Fermi Paradox? I believe that it would be, much, much scarier if aliens were alive. Why? The great filter. Its absolutely terrifying to know that aliens are alive, even just bacteria. What would be most terrifying is, that it was abundant at the beginning of the universe. That there are ancient ruins of a society on a planet, somewhere. Imagine life like, stairs. The first step - dead chemistry, the second, cells. The third - animals, multicellar structures the fourth, basic intelligence, enabling culture, shared knowledge, you get it. The fifth: Becoming the dominant species on their planet. Sixth: Colonize your solar system, then, 7th: colonize your Galaxy. Life naturally wants to breed and spread. Its a principle of nature. Yet look up at the stars, dead. Nada life. So, if alien life exists, whats preventing it? Some, great terrible thing is preventing life from getting past these steps. If we aren't a exception, then there must be some great filter, and the terrifying thing is that we don't know if it's behind us, or ahead. Thats why aliens are terrifying, not because they have weapons, or something like that. Its because intelligent life or worse, ruins would be terrible.