I've always felt that the stronger the case for the idea, the less need to attack the person.
The goal of the comment area is to encourage a wide range of viewpoints, expressed reasonably. A good comment offers a high ratio of substance to rhetoric. Personal attacks on other commenters are inappropriate.
Civility is something that I would rather encourage than enforce. However, occasionally commenters have been banned from posting on EconLog. Each time we have done this, the entire comment section has improved considerably, which leads me to believe that enforcement yields strong positive externalities.