For example, "I think the world was created 6k years ago," is a very non-threatening statement. It's just an opinion and by stating that it's just your thought, you imply that it's okay that others think differently. If you had said, "The world was created 6k years ago," you are stating a fact and inviting disagreement.
It is not about differentiating fact from opinion, but rather not understanding what implications you words have. "Sometimes what wasn't said is more important than what was said." The stereotypical geek might not understand that, preferring a literal interpretation of everything.
Note: I caught myself using, "I think," three times when writing this comment.