There was a recent discussion in the blogging community. A person was making an argument in favor of the Palestinian view that Israel wasn't paying enough attention to civilian deaths and injury at the least and perhaps they were purposely targeting the civilian population. It is not my purpose to take a stand one way or the other on the merits of the argument. The topic is a hot one, emotions run high, and as a result rational thought suffers. This is a tale of the logical fallacy know as Poisoning the Well, in fact in this case the well was poisoned twice.

The proponent of the view presented his arguments and in doing so linked to a photograph of a Palestinian child that had been wounded in an attack. No problem right, certainly a legitimate part of the argument. The problem came with the source. Now I don't know who took the photograph, the actual source of the photo, but I do know that it was found on a racist web site. This was the source of the first instance of poisoning the well. The source of the photo came under immediate attack neither the photo itself nor the conclusions drawn from the photo but only where it was posted.

The result of the link to the photo led to the second instance of poisoning the well. The person that linked to the site came under attack for linking to such a "terrible site". Phrases like beyond the pale, accusations that he was a racist, were used to describe such linking, and from that moment on rational discussion ended. Every time this person posted anything on the subject. Those who disagreed with his view would attack. You can't believe anything he posts after all he linked to a racist site. Very little discussion of issues took place after that, and those that did attempt to discuss issues, usually included or summarized their point of view with the statement. How can you even consider an argument from someone like that? And the second dose of poison, how can you believe anything from a site like that.

There is really no debate any fair consideration of the issues if there is only one speaker and you cut off all discussion with he linked to racist site, consider the source, he’s obviously a racist. It is important to remember that the attack may be true or false, but in either case it doesn't address the argument but rather diverts attention from it.

Those criticizing David Brock sometimes commit a current example of this type of fallacy. Perhaps you've heard of David Brock's Book "Blinded by the Right" the most common statement people make is well he admits he lied in the past why should we believe him now. Should you be suspicious, of course, but base your decision on the arguments he makes and the evidence he presents not that he has lied in the past. It is simply not enough to dismiss all he says with the statement.

Remember that even liars sometimes tell the truth, and even racist sites can make valid points.

A good argument must provide an effective rebuttal to the criticism of or counterargument to the position it supports. Therefore, an argument that inappropriately poisons the source of a counterargument or criticism, and thus prevent it from even being heard or seriously entertained, cannot be a good one.

References:
With Good Reason 6th Ed p 224-227
Attacking Faulty Reasoning Fourth Ed. p 174-176