Sentence Correction (SC) | Re: Economic Vs Economical

If both verbs are in the present tense -- demographers HAVE TO KNOW more than they DO now -- the implication is that both actions are happening in the present.
The result is a nonsensical meaning: how can demographers KNOW more than they KNOW?
To make it clear that the situation is HYPOTHETICAL, the subjunctive is needed: demographers WOULD HAVE TO KNOW more than they DO now.
One purpose of the subjunctive is to convey a situation that is CONTRARY-TO-FACT or HYPOTHETICAL.
The intended meaning
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