Here are the top arguments I know:
- Explicit social contract
You have explicitly consented to have some people rule you - Hypothetical social contract
Something about your behavior suggests that you have consented to have some people rule you, or you would have consented had you been asked - Democratic authority
If enough people agree that X should be done, then X should be done - Consequentialism
We should allow some people to rule others in order to prevent a disaster