This may not be completely what you are looking for since it is not really 'evil', but you might want to look into 'How to win friends and influence people' by Dale Carnegie. It will mostly be useful for unstaged arguments (at work, with family or friends), it will be more limited for staged debates such political debates.

According to Carnegie the way to win an argument is not get into an argument. The reason for this is that you 'win' the argument you won't have convinced the other person of your point of view, you will just make him feel stupid and resentful. Carnegie promotes that you first think honestly about the others point of view since they might be (partly) right. If the other person is so stupid that they can never be right, why are you even bothering to argue with them?

The next step is to agree with the other person on points that you actually agree with. If you don’t agree with your opponent’s points then agree on facts or that something is his opinion. The point is to disarm your opponent with your agreements, since he is expecting disagreement. Now ask questions and make propositions that your opponent will likely agree with. Here you are trying to get him into the flow of saying yes and agreeing with you. Now that the other person feels like you are on the same page he is not really your opponent anymore. You can continue by getting him to agree with the most easy to agree on arguments of your point of view. Move from one argument to the next and before you know it the other person is agreement with your point of view and he is actually happy about it, which means that he is convinced will be supportive.

So covertly manipulating others to accept your point of view without anyone noticing can be quite evil depending on what you have convinced them of.

Obviously this is not really feasible in a staged debate, mostly because the purpose of a debate is not to reach agreement but to impress the public. Though I guess if you were to pull this off in something like a political debate you will have owned it completely because you will have convinced most or all of your opponents of you point of view and their followers will either be convinced as well or have no one left to follow.