Governments do. Laws are enacted with the support of the population that democratically elected the government making those laws.
You bring up "enslavement" and "oppression" - they're not exactly part of the current discussion. Slavery is included in the game, however.
Enslavement and opression have wide meaning touching the subject of freedom, if You use force to rule the force will hit You back, simple law of phisics.
For the first You typed here, no and hell no I will never accept that. Goverments are simply creations and name for unjustice and war and all the is hitting us in RL. People simply go with the Your "law" and "order" rules and kill in the name of whover is in the "top dog" position currently. (aka empire or federation or any other big creation in game)
Freedom means anarchy, no control, no laws of other man imposed on other man, chaos with its own rules but no restriction. Beauty. Freedom is precious, some do not understand that. Some are afraid of it, fear dictates them who they are, fear takes controll of their humanity and their behaviour.
Who told You who can kill and who not, who are You to dictate rules ?
We can discuss it futher, but we running away from the topic i think a little.