Here's an excellent example of the fallacious argument referred to as "guilt by association." The idea is that you develop an association between some evil person and the position you want to attack.
For example, suppose you wanted to show that fundamentalist Christianity was bad. What you do is find some fundamentalist Christian who behaved immorally—not hard to do—then allow readers to draw the "obvious" conclusion.
Or, you could do the same thing with those who accept evolution as Barry Arrington does on Uncommon Descent [Darwin at Columbine Redux].
As the attorney for the families of six of the students killed at Columbine, I read through every single page of Eric Harris’ jounals; I listened to all of the audio tapes and watched the videotapes, including the infamous “basement tapes.” There cannot be the slightest doubt that Harris was a worshiper of Darwin and saw himself as acting on Darwinian principles. For example, he wrote: “YOU KNOW WHAT I LOVE??? Natural SELECTION! It’s the best thing that ever happened to the Earth. Getting rid of all the stupid and weak organisms . . . but it’s all natural! YES!”For the record, I reject all attempts to discredit Christianity by pointing to priests who molest children; the fact the Kent Hovind is in prison; or the tribulations of Jimmy Swaggart. We can gloat about those incidents and revel in the hypocrisy but they say nothing at all about the truth of Christianity.
Elsewhere he wrote: “NATURAL SELECTION. Kill the retards.” I could multiply examples, but you get the picture.
It was no coincidence that on the day of the shootings Harris wore a shirt with two words written on it: “Natural Selection.”
I am not suggesting that Auvinen’s and Harris’ actions are the inevitable consequences of believing in Darwinism. It is, however, clear that at least some of Darwin’s followers understand “survival of the fittest” and the attendant amorality at the bottom of Darwinism as a license to kill those whom they consider “inferior.” Nothing could be more obvious.
Similarly, I do not apologize for nor condone the behavior of stupid people who accept evolution. It's irrelevant to the debate over the facts of evolution.
Everyone should adopt this position. Unfortunately, there are quite a few people on the other side who get all uppity whenever a Christian is caught with his pants down but see nothing wrong with blogging about evil evolutionists.
The word you're looking for is "hypocrisy." It seems to be quite common on that side of the debate.