Truly, the growth of soccer as a competitive professional sport has been astronomical since the birth of MLS. It doesn't seem like it's come all that long of a way... but it really has. To the point where the momentum is very considerable now... I truly believe that in the next 20-30 years, soccer will become every bit as much a major sport in this country as football, basketball, and baseball are.
But that's just my opinion.
The big thing about youth soccer is that in America it's primarily an upper class sport.
Football can be, as well as baseball. Tennis and golf definitely are.
But we have evidence from other countries that it doesn't HAVE to be an upper class sport. Indeed, it's very popular in the lower classes of a lot of third world countries. Why? Because it's something kids dream about.
I believe that as the sport gets more popular and becomes more visible to the lower classes, it will be just as popular. But just like any sport, there will always be an advantage to those that can afford to put their children in specialized training programs and competitive leagues - just like basketball and baseball.
Basketball (same for Football) programs take kids in, I think mainly through shoe sponsorship money. Soccer is pretty much paid for by the parents of the kids. Third world countries arent turning out a lot of top soccer players, the big nations are who have these huge soccer clubs that fund youth development like Nike/Adidas/UA fund youth development basketball in the USA.