D. They may take the author's argument less seriously.
Explanation:
When exposing your own ideas, in oratory or textual form, you should be careful in how you address those who oppose you or are in disagreement of you since, gratuitously attacking your opponents —like calling them slobs— without offering arguments for the attack itself may only alienate those who are already in disagreement with your argument to begin with. An argument should stand on solid arguments and not on any form of attacks, personal or otherwise.
