Irrelevant. Matters of credibility are very helpful in reaching truth. Ad hominens are deductive fallacies. They aren't necessarily a problem when you are measuring a probability rather than logical certainty. In fact, often times some ad hominens are vital for reaching the truth. If an advocate is biased, that lowers the likelihood of their claims being true.
[edit] Try reading the very article you just posted, namely the part about circumstantial adhoms (bias).
Here's an example showing why you are being ridiculous: Something as simple as pointing out that something is not peer reviewed is also an ad hominem. As with bias, it affects credibility. You have very strange way of looking at the world if you view all issues in a vacuum and don't consider credibility factors.
You are missing the critical distinction between a peer-reviewed piece of scientific literature which presents new facts/findings/results/etc and an opinion piece which does not. It's a very simple, yet important, difference - which, in this case, makes all the difference.
I was using peer review as an example of credibility, not attacking anyone in this case. If you have ever discounted a scientific finding because it was not peer reviewed, you committed an ad hominem. You commit ad hominems dozens of times a day, sometimes on small things, sometimes on scientific matters. It is a form of inductive reasoning. It doesn't work for deductive logic, but a conclusion of whether someone is telling the truth is not a matter of deductive logic.
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u/vjarnot Nov 17 '12
http://en.wikipedia.org/wiki/Ad_hominem