Focus on the problem, not the people. Any scholar in negotiation will tell you that.
A vendor at the flea market is an unkind bastard. But if you need some art and he is trying to sell you his, you discuss the problem and try to make a deal. Another piece of perfectly fine art is available at the next booth.
Your boss is cheap. But if you need a raise and they are trying to keep you on their team, you discuss the problem and try to make a deal. Another perfectly fine, better paying position is available down the street.
A belligerent regime runs a powerhouse in the Middle East. But if you want their nuclear weapons program scaled back, you focus on the problem and try to make a deal. Weapons grade uranium is bad in the wrong hands.
If you want to negotiate to mutual interest, you focus on the problem, not the people.
For someone trying to defend the US’s recent nuclear deal with Iran, this would be their argument. They were not focused on the untrustworthy, Israel-hating, terrorist loving regime. They were focused on the problem.