We feel that replying to the lsit subscribers directly defeat the purpose of the mailing lists, which is to facilitate and open public discussion for all members to participate in. We have run our lists both ways, and we feel this is the better configuration.
If you wish to reply to the a list subscriber directly, reply to the message and copy/paste the intended list subscribers email in place of the list address in your mailers "to" field. We feel that unless there is an overriding reason, the choice of whether to reply privately or to the list should be left up to the author of a message. The feedback we've gotten and the user surveys we've taken also show that more of our users want the lists configured this way.