Institutio Oratoria

And yet there are some who take pleasure in directing their onslaughts against their opponents' counsel as well, a practice which, unless they have deserved such attacks, shows an inhuman disregard of the duties incumbent on the profession, and is not merely useless to the speaker (since he thereby gives his opponent the right to reply in the same strain), but contrary to the interests of his case, since it creates a hosthe and antagonistic disposition in the advocates attacked, whose eloquence, however feeble it may be, will be redoubled by resentment at the insults to which they have been subjected.