The Founders of America understood something that collectivists deny: human nature cannot be changed.
People are not angels. They pursue their own interests. They can be selfish, greedy, ambitious, and cruel. No system can make them otherwise. Every attempt to create the "New Man" — Soviet, Maoist, Cambodian — has produced not transformation but terror.
The Founders did not try to change human nature. They designed a system that works with it.
Rights come from God, not government. If rights come from God (or nature, or simply exist prior to government), then government cannot legitimately take them away. If rights come from the government, then the government can revoke them at will.
Powers are limited and enumerated. The Constitution does not list what citizens can do — it lists what government can do. Everything not listed is forbidden to the government, reserved for the people.
Power is dispersed. Federal, state, local. Executive, legislative, judicial. Each checks the others. No one can accumulate enough power to tyrannize. This is messy, slow, frustrating — and intentional.