Well, rhetorical questions -questions posed for rhetorical effect rather than for the purpose of gaining an answer - often don't end in a question mark. For example,
 Darcy points out that Mr Bennet has acted with impropriety, but does the reader have to agree with this statement.
=> Without the question mark, "but . . . ." means, Darcy can be pompous, so the reader doesn't always agree with Darcy's point of view.
 Her family doesn't always behave well, especially at the Netherfield Ball, but does he have to keep reminding her about it.
=> Without the question mark, "but . . . . " means, it's rude and utterly mean of him to continually remind her about her family's behavior.
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