I've noticed that a good thread often deteriorates in one of three ways

toilet humor
caviling over English usage and spelling
politics

For example, look at the thread on the bridge collapse in Minneapolis. I posted some technical information, much of it reassuring to the general population. What follows are mostly smart-alec posts criticizing politicians.   

Setting aside the snots who ridicule someone's English usage, among the threads that stayed on topic longest and were the most enjoyable were threads about language. I believe Mudcatters talk about language more than anybody.