If this is true (https://en.wikipedia.org/wiki/Legacy_preferences#Economic_impact https://en.wikipedia.org/wiki/Legacy_preferences#Economic_im... suggests it's

If this is true (https://en.wikipedia.org/wiki/Legacy_preferences#Economic_impact https://en.wikipedia.org/wiki/Legacy_preferences#Economic_im... suggests it's disputed), the effect is probably marginal, and in any case, Harvard has the largest academic endowment in the world. It seems unlikely that it needs legacy admissions to stay afloat.