If you just bought, you don't have a negative real interest rate.
Your interest rate is probably 5% or so?
The real interest rate is probably 3% or so. That means your REAL interest rate is 2%.
When you inevitably get the chance to refinance at below 3% - your REAL interest rate will be negative.
The 30-year fixed mortgage is a product that would not exist without a government guarantee on Fannie & Freddie's debt. Even if you have a jumbo loan - it's only because of the MBS market created by Fannie & Freddie.
In essence, the tax payer is paying you for you to have a mortgage on your house - regardless of whether Fannie securitized your mortgage.