People who use poor logic usually do so out dishonesty. I'm not talking about individuals who may be feeble in thought, but about ideological leaders and those who have been through rigorous debate.
This is just a portion of who is in view thought. I agree some are intentionally dishonest, but I think most actually think their reasoning is sound.
There are some great philosophical and theological questions, but most things are rather simple. OJ did it.
Here is the thing: I look at it as most draw conclusions on limited information. Because they are predisposed to a particular faith, group, or Theology, they examine that issue through the lens which has been supplied to them. For example, the person going to a fellowship where free will is taught may be, on a regular basis, exposed to verses or passages that indicate man's choosing. Those opposed to it exposed to teaching that centers on God's choosing. And because it is necessary, in Theological Debate, to proof-text (have a Scriptural Basis for) the view, a very reasonable case could be made for both. And that is how most draw conclusions: they present only that which seems to emphasize their own view, but they do not deal with those passages which seem contrary.
Probably the best example is whether salvation can be lost. There are numerous passages which seem to indicate men can lose their salvation. Many who believe salvation cannot be lost center on passages that seem to make this clear, yet, when certain passages are brought up they are unable to reconcile those passages because they do not understand them. The same is true for those who actually use those passage to "prove" salvation can be lost...they simply do not understand the passages. They use them out of context because usually the fellowship where they attend does this. They sit under countless messages where it is taught that, for example, the Christian who commits willful sin can lose their salvation. And when they study, they look for more...proof-texts. And because they are predisposed to a certain view, they are often oblivious to anything that might be seen as dismantling their own view.
And the bottom line is that this is not really a matter of dishonesty, they think they are presenting the Biblical truth. I think most have to take for granted that the leadership they are under is correct, and I doubt very many intentionally sit under leadership they know to be in error. Church-Hopping is an example of people leaving a fellowship because they disagree with what is being taught (though we also see emotion as a leading factor in this too).
As far as OJ, a decision on his guilt or innocence is no different than what we do when we seek truth from Scripture. We examine the evidence, and sometimes the evidence is overwhelming. If there is an emotional attachment, though, the evidence might be overlooked. Again, I don't see that as dishonesty, just poor judgment.
God bless.