Do you want to be great (or at least attempt to be great)? Then you MUST specialized (except for 0.00000000001% of people). And start in the womb. Tiger Woods, Mia Hamm. . .
Do you simply LOVE being athletic and enjoy sport—but have no urge to be the very best? Then play all the sports you can.
In other words, there is no one answer. If a child is gifted early enough to notice, and some (reasonable) adults can see that talent, I believe in focusing, specializing for the potential of greatest few people reach. But it all depends on what you want to achieve.
I think soccer requires such high skill to excel that it is more likely NOT to have multi-sport athletes.
