I'm not sure there's anyone here who makes that argument.
Some people don't like the sport, and that's fine. I think part of that is just that many in the US didn't grow up with it as an option. Baseball is accepted for what it is because we all have memories of playing Little League and watching major league players hit it out of the park as kids.
But the sport is definitely growing among young people in the US (fastest growing sport among youth in the nation, and more popular than baseball with the under 25 crowd), and it's a great move for the future of sports in the city of Indianapolis to put a premium on it before it gets really big. (That is, if you believe that big time sports encourage the growth of a city, which Indianapolis clearly does with Lucas Oil and Banker's Life.)
The decline of the Euro is going to lead to some big time players moving to the US, so expect further growth of the sport.
I don't think that "doomed" is accurate. Lucas Oil cost ten times what than this stadium will, and it doesn't host as many events per year. You can absolutely make the argument that the Luke brings in more money to downtown, and would be right on that. But in terms of breaking even on the initial input cost, it's probably just about as likely.
Point is - at that point, it's not a "soccer is dumb" argument - it's a "public financing of sports stadiums is dumb" thread. Which, in my view, is a more appropriate and reasonable argument.