Treat users like ignorant entitled idiots, and they'll just continue to act like ignorant entitled idiots. Meanwhile everyone else who does know what those settings are for suffers, and it decreases the chances of future users ever learning they could do that.

If users aren't putting in the effort to read warnings/error messages, or can't put two and two together and correlate why things aren't working on some sites with what they did with the settings (or even better, apply some more critical thinking and possibly Googling to figure out why), I think that's a sign of a deeper problem and trying to patch over it by dumbing down software interfaces is a horrible direction to take.

To become knowledgeable users of Web technologies and not mere consumers, they must be allowed to explore, experiment, and break, then fix things. Taking away these settings discourages that. "The only real mistake is the one from which we learn nothing."

FYI Alex Limi no longer works at Mozilla.