The vast majority of debts currently held in the premier league i would say are "bad". Im not a buisness whiz (in fact my buisness sense is shit) but just look at how it currently stands,
club debt. Only 6 clubs have an operating profit, and correct me if im wrong but it seems judging from a lot of clubs operating profit and interest payments, its really fucked. Now most of these clubs are in this mess directly relating to wages and transfer related business. I should say though the premier league is an extreme example and the worst in regards to debt in europe.
My knowledge of the NBA and NFL doesnt go beyond knowing how to play the sports. However i think im right in saying there is no relegation in those sports. This is a very important point. When a team in european football reaches the highest league, its profit usually increases because of better TV deals, coverage etc. In some countries the difference is negligible. In others, mainly the bigger leagues the difference its incredible. In England, relegation from the premier league causes a average football club to lose in the region of 50million pounds a year in tv deals alone (the second league under the Premier league gets on average only 1m). So clubs will do everything once promoted to the Premier league to stay in the Premier league. Including paying ridiculous wages and salaries. The clubs pay a lot to first get into the premier league through promotion, they pay even more so the dont get relegated, they then go into debt and try to climb up the table by paying more and more, until they cannot sustain it and they collapse. Im sure you can see, its a vicious cycle. While its still usually only to the mid to smaller clubs (only Leeds united are the only big club thats fallen that way in recent times). Its could happen to the bigger ones aswell in lesser way. Example liverpool right now. This adversely affects the league.
This is why the Premier league is more vulnerable compared to those american leagues, the clubs are caught in a cycle of debt and more debt causing the whole league to be unstable. There is not such thing in America. The "franchises" are not relegated, nor is such extreme financial consequences put on them for not performing on the pitch. Its even fairer with the picking of upcoming talent (another thing that is totally fucked up in football), so there is always chance of improvement.
Coincidently, if on of those American leagues become unsustainable im sure it will be bailed out, or a new league formed. They're essentially the only major leagues in their sport. Without them there is no sport. Not the same in football. If the Premier league collapses, its englands problem to fix. Football will continue. Your last point is interesting though, i agree with you clubs shouldn't be stupid and pay over the odds. The thing is, football clubs are
run by idiots.