Men fear thought as they fear nothing else on earth, more than ruin, more even than death
I don't think that's true. In fact, it sound close to "Well, if those people don't agree with me, it must be because they are afraid of my thoughts!", which is a convenient excuse to ignore other people's opinions, with an implicit ad hominem ("They must be disagreeing with me for irrational reasons!").
If you don't agree with me, you're probably just afraid of my ideas.
I think the reason you can tell that people are afraid is because they start getting angry at what you have said. The more the discussion occurs the angrier they get. If you're not afraid, the expected response would be interest (why do you think that?) or boredom. Many discussions become angry, so I suggest most discussions are frightening and by extension the thought that caused the discussion in the first place could well be scary all by itself.
This is our monthly thread for collecting these little gems and pearls of wisdom, rationality-related quotes you've seen recently, or had stored in your quotesfile for ages, and which might be handy to link to in one of our discussions.