They are right to the some point. In nature, there are predators and those who are hunted. Survival of the fittest is a law of nature. It leads to evolution which leads to developing of all life. That is how humans came to be and that is how life forms survive through million of years. That is the way of life. To ask of someone to be completely selfless is and impossible thing. Humans (humanoids in GFFE) have that instinct inside them. An insting to do everything to survive. That is the law of nature. Eventualy, humans have developed something called conscience, but deep inside us lies that law of nature. Sith rely on that, use it for strenght. They are closer to nature than others, especially the Jedi who even deny their feelings, but I don't agree with their actions.