Some people in politics are just bad and if you are friendly with them then at the very least you are indifferent to their badness. Sure sometimes people in DC genuinely have to work together, make those legendary deals, GET THINGS done, but there's no need for these relationships to go beyond the professional, beyond the small bit socializing professional relationships can require. If your friend is a monster, what are you doing?
No you can't choose your family and to some degree you can't choose your "old friends," people you knew in high school or college and then traveled very different paths in life. You know, those people on facebook who make you mad. But later in life you have the power to pick and choose.