> having the government stop subsidizing the mortgages of investment properties (e.g. only one mortgage subsidy is available for each family).

I think you are confusing home loans (which are subsidized) and business loans which are not subsidized).

Fannie Mae/Freddie Mac loans are only on 1 primary home and 1 secondary home for individuals. These loans are limited and really don't work in high property value states. You should google the difference between "conforming" and "non conforming" loans.

You might be thinking of the mortgage deduction on the income tax. Trump already did this. This only hurt young people in high property value states.

Business real estate loans are more expensive because they are not subsidized. However, businesses do pay taxes only on earnings (income-expenses). Loan payments are expenses that reduce the earnings. Good luck on getting rid of business expenses. Yang proposed changing the tax law because of this.

All this means your proposal would have a very limited impact. It would only hurt individuals who live in an expensive property where the homeowner has mostly paid off their mortgage (old people) and used the principal to buy a rental (up to 750k).