Various forms of personal attacks (ad hominem) in which a person or group is disparaged by being unjustifiably associated with another person or group that is viewed negatively.
Example:
Hitler was a vegetarian (and committed terrible crimes).
PersonAis also a vegetarian.
Therefore, PersonAholds criminal views similar to Hitler’s.
Clearly, Hitler’s vegetarianism is not one of the aspects of his character that is generally deemed criminal, and there is also no reason to assume that it had a direct influence on the crimes committed by him and his followers. To suggest that this particular commonality is in any way an indication of a connection between A and the Nazis is plainly absurd.
If such an association is intended as an attack on the person, it constitutes an ad hominem attack; at best, it is still a (rather crude) diversionary tactic (red herring).
The basic form of each of these attacks is:
Xis a property ofY(andYis viewed negatively).
Zalso has the propertyX.
Therefore,Zis likeY(and should also be viewed negatively).
Although this fallacy is typically used as a personal attack on the opponent in a discussion, there are also situations in which it is used as a “knock-out argument” – supposedly relevant to the issue at hand, but in an unfair manner.
Xis an argument thatYalso used
(andYis viewed negatively).
Therefore, argumentXis false.
However, it is clear that an argument does not become invalid simply because it has already been put forward by someone else, no matter how unsympathetic, immoral, or even criminal that person was or is.
There are situations in which referring to an association with a group or another person can be a factually justified contribution to the discussion.
(1) This is particularly the case when the person being criticised acts of their own accord as a representative of the group in question. This would be the case, for example, if a minister had to justify the government’s or his party’s mistakes, or if the team captain had to account for the football team’s poor performance.
The principle of voluntary self-association definitely excludes all groups to which one is assigned without having a genuine choice – or which, at the very least, cannot be changed without considerable effort. These include, for example, ethnicity, skin or hair colour, mother tongue(s), religion, nationality, place of birth, height, disabilities or special talents, etc.
(2) Furthermore, it is a prerequisite that the group with which negative associations are linked (assuming it is not simply a single person) is defined narrowly enough and clearly enough to actually capture the negative aspects.
It is certainly not fair to hold every Christian responsible for all the wrongdoings of Christianity – just as, indeed, it is not fair to hold individual Muslims or Jews responsible for things that have been or are being done in the name of their respective religions.
If, on the other hand, a particular sect or organisation has behaved in a particularly negative manner, it is justified to associate anyone who identifies with such a group with it.
Applied to politics, this means, for example, that membership of a terrorist organisation or a radical party (regardless of its political orientation) provides a valid basis for negative association, whilst a vague and broad definition of a group (such as “the Right” / “the Left” / “the Liberals”, etc.) is too broad and too vague.
In any case, however, the basic requirement remains, of course, that the topic raised is relevant to the subject under discussion and is presented in a fair manner.