I see that my conception of the "principle of charity" is either non-trivial to articulate or so inchoate as to be substantially altered by my attempts to do so. Bearing that in mind:

The principle of charity isn't a propositional thesis, it's a procedural rule, like the presumption of innocence. It exists because the cost of false positives is high relative to the cost of reducing false positives: the shortest route towards correctness in many cases is the instruction or argumentation of others, many of whom would appear, upon initial contact, to be stupid, mindkilled, dishonest, ignorant, or otherwise unreliable sources upon the subject in question. The behavior proposed by the principle of charity is intended to result in your being able to reliably distinguish between failures of communication and failures of reasoning.

My remark took the above as a basis and proposed behavior to execute in cases where the initial remark strongly suggests that the speaker is thinking irrationally (e.g. an assertion that the modern evolutionary synthesis is grossly incorrect) and your estimate of the time required to evaluate the actual state of the speaker's reasoning processes was more than you are willing to spend. In such a case, what the principle of charity implies are two things:

• You should consider the nuttiness of the speaker as being an open question with a large prior probability, akin to your belief prior to lifting a dice cup that you have not rolled double-sixes, rather than a closed question with a large posterior probability, akin to your belief that the modern evolutionary synthesis is largely correct.
• You should withdraw from the conversation in such a fashion as to emphasize that you are in general willing to put forth the effort to understand what they are saying, but that the moment is not opportune.

Minor tyop fix T1503-4.