There would never be a "permanent" deferral of a draw acceptance - for exactly the reason you give: there would be no incentive to offer a draw. The solution is to have a temporary draw acceptance. This would be for a limited number of grace moves which would act as a disincentive to offer a draw. The only purpose in offering a draw is if it were objectively justified.
For players of modest ability, a single grace move would be effective in reducing draw offers. This would cover the majority of players. Hence the rules of chess could be modified to include a grace move.
For competitive chess, a single grace move would be of limited impact. A more suitable number would be 3 grace moves, since this corresponds to the average look-ahead by grandmasters.
Actually it would be possible to calculate accurately the precise number of grace moves required by grade of player once we have a database which includes draw offers. Unfortunately, although players are obliged to record a draw offer (thank you Stewart Reuben) the pgn files do not show these. It would be fascinating to see what happens after a draw offer aggregated over all games.
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