Knowing some basic rules of communication might be useful. Here is what is said about personal attack, referred to as ad hominem – to the person.
Ad hominem argument, argument to the person or against the man: Replying to an argument by attacking to the person making the argument, rather than by addressing the substance of the argument in an attempt to discredit that argument.
Ad hominem fallacy: To assert that someone’s argument is wrong purely because of something discreditable about the person rather than addressing the soundness of the argument itself, in order to discredit the person, and, specifically, to invite others to discount his arguments.
You claim that this man is innocent, but you cannot be trusted since you are a criminal as well.
Not all ad hominem fallacies are insulting: Paula says the umpire made the correct call, but this can’t be true, because Paula was doing more important things than watching the game … even though it is saying something positive about the person, it is addressing the person and not the topic in dispute.
Ad hominem abusive:
Insulting or pointing out character flaws or actions which are irrelevant to the opponent’s argument. Insults and even true negative facts about the opponent’s personal character have nothing to do with the logical merits of the arguments or assertions.
This tactic is frequently employed as a propaganda tool among politicians who are attempting to influence the voter base in their favor through an appeal to emotion rather than by logical means, especially when their own position is logically weaker than their opponent’s.
Candidate Jane Jones’ proposal X is ridiculous. She was caught cheating on her taxes in 2003.
Ad hominem circumstantial: Pointing out that someone is in circumstances such that he is disposed to take a particular position. The opponent’s bias is not necessarily irrational, but neither is it strictly correct according to logic: He’s physically addicted to nicotine. Of course he defends smoking!
Ad hominem tu quoque: An irrelevant accusation of hypocrisy, inadmissible in legal and scientific debate, distracting from the business of politics: A corrupt lawyer who prosecutes embezzlers may be behaving hypocritically, but this does not weaken the evidence he presents against the accused.
Guilt by Association: To attack a person because of the similarity between the views of someone making an argument and other proponents of the argument.
You say the gap between the rich and poor is unacceptable, but communists also say this, therefore you are a communist, or: You say the gap between the rich and poor is unacceptable, but communists also say this, and they believe in revolution. Thus, you believe in revolution.
A similar tactic may be employed to force someone to choose between renouncing an opinion or admitting membership in a group: You say the gap between the rich and poor is unacceptable. You don’t really mean that, do you? communists say the same thing. You’re not a communist, are you?
Guilt by association may be combined with Ad hominem abusive: You say the gap between the rich and poor is unacceptable, but communists also say this, and therefore you are a communist. Communists are unlikeable, and therefore everything they say is false, and therefore everything you say is false …