Thanks for the detailed reply - I'll try to respond to each of your points.

First of all, using dark arts does not imply you have to tell outright lies.

Secondly, you say "if a person ends up with better ideas but all the same biases, their heads can later just as easily be filled with whole new sets of bad ideas by other Dark Arts practitioners." When the alternative is that they only had bad ideas in their head, this is a still a win. And your example is the minimum win possible. What if we used dark arts to help someone remove a cognitive bias? Is it now justified?

Third, PZ Myer chose a very effective persuasion strategy, The Admirable Admission Pitch. However, one case where someone was effective sans-dark arts hardly proves the sans-dark arts approach is optimal in general. When you look at a heavy-weight persuader of the world like Al Gore, you can see he makes heavy use of the dark arts.

Finally, you're correct with respect to the problem you pointed out in your 1st paragarph. I'll tweak the post to fix it.