Your question is fair enough. However, I do have some major problems with the self-defense side of BJJ.
A lot of people use sport BJJ to refer to the new school competition style and street BJJ to refer to the old school style taught by Helio, Rorian, etc. Street BJJ is thought of as keeping a tight closed guard to avoid strikes, controlling the arms during guard passing to avoid strikes, stalling a lot and waiting for the opponent ot make a mistake, etc. The problem is that this stuff is not street effective at all. In fact, I dare say that the faster paced sport BJJ is more effective.
Despite what Helio says, BJJ was never developed for self-defense. The self-defense aspects of BJJ (see old Gracie Jiu-Jitsu tapes for old school self-defense techniques) would be better covered in a judo class. The main difference between BJJ and judo is the heavy focus on groundfighting. And such a heavy focus on groundfighting is not very practical for the street.
Helio made his career out of winning vale tudo fights, not self-defense. He did this primarily by using his guard to tire out his opponents in marathon matches hours long. He would then force them to make a mistake and get a submission. Nowadays with time limits this strategy doesn't work anymore. Helio and his supporters say this waters down the self-defense aspect.
How is it self-defense to fight someone 1v1 for hours, without any weapons, friends who jump in, or police to break it up? That is competition, not self-defense. Calling old school BJJ self-defense is a joke.
Modern sport BJJ is actually more practical for self-defense, in my opinion. I say this because it is more active and focuses on attacking with a sweep or submission quickly rather than waiting for the opponent to give you an opportunity. In a self-defense situation, there simply isn't much time to do anything on the ground. Therefore I think the sport BJJ attitude is better.
