Dark forest theory-
All life desires to stay alive.
There is no way to know if other lifeforms can or will destroy you if given a chance.
Lacking assurances, the safest option for any species is to annihilate other life forms before they have a chance to do the same.
Since all other lifeforms are risk-averse and willing to do anything to save themselves, contact of any kind is dangerous, as it almost assuredly would lead to the contacted race wiping out whoever was foolish enough to give away their location. This leads to all civilizations attempting to hide in radio silence.
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