This discussion is of "rebuttals," the part of a paper that attempts to disarm the opponents' arguments. Sometimes, the rebuttal section should come before the arguments supporting your position and sometimes after: that is a decision to make after you have written the various sections of the paper. For now, concentrate on writing a rebuttal.
Rebuttals, by definition, simply try to diminish the power of the opponent. Normally, people consider a rebuttal that relies on reason (logos) to be more ethical than one that relies on emotion (pathos) or on personal attack (ethos). But, some of the ancient rhetoricians seemed to think it was okay to use all of these strategies.
Arguments Based on Logos (Reason)
When you try to refute the reasoning of someone, you try to show one of the following:
Arguments Based on Pathos
Although rebutting someone using emotions is sometimes considered unethical, the use of pathos is not inherently wrong. Suppose that your opponents' policies will result in the suffering of others. Simply pointing out the possibility of suffering is not as effective as actually saying something like, "Let's consider the case of Janice if these policies are put into effect." Then you would go on to tell a story about Janice in some detail. The emotional tone of the story may be a more effective rebuttal of the opponent than several arguments based on logos.
Arguments Based on Ethos
Rebuttals based on ethos are the most likely to be unethical. Such an argument attacks the character of the opponent directly without dealing with her position's logic. This argument is sometimes call the ad hominem argument, meaning "against the man." Normally, it is listed as a fallacy, and students are encouraged to point out that their opponents are employing a fallacy. It is the use of such arguments that cause politicians to cry out that "negative political ads are destroying the political process."
Certainly, one should avoid attacking someone else's character if at all possible, but there may be some occasions in which discussion of your opponent's character is appropriate. It's almost impossible to give rules of thumb about when it is permissible and when it isn't. There is much debate among ethicists about this very issue. Does someone's personal life have anything to do with whether or not people should support his or her positions? Why or why not? I'll leave that up to you to decide.