If I have the freedom to kill an entire city, will I have the freedom to spare some orcs ?
Hopefully. There is at least one 'boss' fight you can avoid by talking your way out of (though with a spider queen) and a group of goblins can be friendly or hostile depending on how you approach them and your actions earlier in the game. One of the preview videos did show a brief section with some non-hostile orcs, but avoided spoilers so I don't know what the situation was.
