I find the use of an alleged “motivation of your opponent” as an argument against his case to be rather boring and persuasive only to those who desperately want to believe. The idea is: Don’t argue that the opponent's case is invalid, argue that the opponent’s motivation is nasty. I suppose that it is a subcase of the abusive ad hominem argument: A fallacy which usually involves attacking the traits of an opponent as a means to invalidate their arguments. In this case the opponent’s motivation is the particular aspect of the person that is attacked. The merits of the case, one way or another, often get lost altogether. Of course, if you don’t have a good case, then perhaps avoiding an argument based on merit is your best chance. (Did I just slip into the motivation fallacy?)
The place this is currently getting a lot of play is in the Voter ID laws. Those Rs are just trying to deny the right to vote of the old and poor who are expected to vote Democratic. The D’s are just trying to fix it so all of those illegal aliens can vote for them. Both arguments totally ignore the fundamental question:
A. If a person claims to have a right or an entitlement to something, should they
1) have to demonstrate that they are eligible for that thing or
2) should the government grant these rights and benefits on the honor system.
B. Since voting is essential to a democracy it gets special treatment. There is a fundamental obligation by the government to ensure there is no impediment (other than eligibility) to the exercise of the right to vote. In particular there can be no financial impediment – tax, charge, or cost (24th amendment). That is, if you require a picture ID, then you must provide a way for them to get one cost free.
I choose A1 and B. A1 it seems to me is self evident. B is a bit harder to implement, but not really that bad.
Don’t misunderstand me. I am not saying either group does not have the alleged motivations. I am not saying that motivations are not important. They may explain why someone is taking a certain position.
But an argument based on the opponent’s motivation is not valid. There are at least two good reasons:
1. Even if their motives are bad the result could be good.
2. Unless you are God, you don’t know their motives.