Who says NFL stadiums can't be built without public subsidy? Of course they could.We can argue in the weeds, the point is there are many, many events being held in the new stadium for which the people who profit off them could have been partners with the Wilfs/Vikings. The fact that stadiums as high-end as the ones currently being erected cannot be fully paid for, even after the NFL "loan," without public subsidy is proof that the value in the price tag is not worthwhile to Vikings fans or other sport/concert/show goers. (That, or the NFL owners outside of Atlanta are really good at convincing the public to pay a larger share than is necessary for the stadium to be financially viable).
Public money is involved because sports teams have created that precedent over many years. And because public money has allowed teams to build nicer stadiums than they could have built privately, the standard for stadiums is now higher than the market value. The Vikings could have put together a new field and four sets of bleachers for $500 million, but without the public subsidy it would not be competitive in today's NFL.
It's a vicious cycle, and fixing it has to come at the national level, not some pipe dream that a non-existent MLS team and a monster truck promoter will step up to make up the difference.