Apart from the possibility of Michael having a personal grudge against one of the members, there are several other possible explanations, for example:
The difficulty of putting an exact limit on when it is "too much".
Not noticing an insulting message in a timely manner (it doesn't seem to make much sense to start complaining months later).
Subjective evaluations on the severity of an offense.
And, perhaps the members in question have indeed been warned.
So, even if you think that Michael's decision is wrong (and perhaps it is, but that is not the point here), there is really no need to doubt his motives, if the (possible) error can be explained in many different other ways.
However, I do think that measures against obscenity (among others) should be more systematical.
>And now I see according to message #943800 that there have been others who have violated your rules, but you seem to be selective in applying them. Or was it John's comments regarding the French language? Got a question for you, Michel. What if your rules said that African Americans could not participate? Or that anyone who used the phrase "The French are losers" was against the rules? That would be ok? Where do you draw your subjective line? All this crap about "It's my site and we will do what we want and do not have to explain ourselves" is just that. Crap.
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>UPDATE: Or message #352360 or message #354011 after just a quick seach. I'm sure if I looked for more words/phrases/offending/sensitive messages I would find plenty.
Difference in opinions hath cost many millions of lives: for instance, whether flesh be bread, or bread be flesh; whether whistling be a vice or a virtue; whether it be better to kiss a post, or throw it into the fire... (from Gulliver's Travels)