Diane Feinstein believes that every American who isn't a cop or politician is a violent criminal who hasn't been caught yet, and thus believes that only cops and politicians such as herself should own firearms... I don't see any conservatives standing up to defend her...
I think what you really meant to say there was "why do conservatives always defend the rights of people I decide not to like?" The answer to which being, they don't, but that's the perception you choose to have based on your particular, subjective view of reality.