(e.g. "clouds lead to rain", "fire is hot", et cetera).
I suspect the kind of opinion the quote is talking about is as defined here; a belief or judgment that rests on grounds insufficient to produce complete certainty. Neither “Fire is hot” nor “Clouds lead to rain” count as examples of this as most people have a fair amount of evidence on hand to back those beliefs up.
In light of this, could you please provide alternative examples of conventional opinions that were also held in the past?
I suspect the kind of opinion the quote is talking about is as defined here; a belief or judgment that rests on grounds insufficient to produce complete certainty.
Adherents of rule #1, however, will never have grounds sufficient to produce complete certainty, in which case, "fire is hot" is an opinion by that definition.
However, a a pure counterexample rather than a mere logical knot:
could you please provide alternative examples of conventional opinions that were also held in the past?
Sure. "Murdering your brother out of jealousy is wrong." That's a fairly conventional opinion, no?
Betrand Russell's Ten Commandments for teachers.
I find this to be of use not just for teachers but for rationalists in general. #8, especially, is an especially eloquent formulation of Aumann's Agreement Theorem.