If the person doesn't get the point after your 2nd response - their probably NOT a FREEPER! More likely it's a DU lurker!!
And ... I don't think there is any moral or otherwise requirement about responding. We are all here voluntarily! If you don't like a response - you can reply or ignore it. If it's over the top - you can report it. Otherwise, it should be everybody's choice to respond or not.
I don't understand. Can you be more specific?