Maybe you and I are debating two different things. 

Fedimints do not increase Bitcoin supply. 

Fedimints take Bitcoin and turn it into ecash tokens that may be claimed for Bitcoin in the future. Fedimints may make more claims than they have Bitcoin. At that point the Fedimint is fractional reserve on the ecash. Some users will go to claim their Bitcoin and it won’t be there. To an regular user, their Bitcoin is gone.