To what extent is it acceptable for someone to present an opinion on something

To what extent is it acceptable for someone to present an opinion on something

To what extent is it acceptable for someone to present an opinion on something of which they have no first hand knowledge? Specifically, if someone has an opinion about an author without having read any of their books and only having heard others speak about them, are they still entitled not only to an opinion about said author, but also for their opinion to be taken seriously? Alongside this, if we can have an opinion about something for which we cannot have first hand knowledge (e.g. the French Revolution) but only through information we have read in historical accounts, does this imply that we do not need first hand knowledge at all?

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