That everyone is human and should be treated as such why can't everyone else do that.
because it's easier to do bad stuff to people (invade another country, take people as slaves, scapegoating etc.) when they are othered, made to seem different. If they aren't the same as you they don't have to be treated the same as you. That's why its important to spot fear-mongering when it's happening "Why are they making me see this person/people as different?" "Why do they want me to fear them?" "What is the speaker to gain if I fear them?" (Acceptance of a war/invasion, limitation of their human rights etc)
He's sleeping with his friends girlfriends because his friend did. He loves his friend and that's probley as close as physical contact sexually he I'll get with his friend for now. Both are still to immature to deal with a relationship ┑(￣Д ￣)┍