A little more on the history and development of Krav Maga. Imi Lichtenfeld grew up in Germany during the rise of Nazism. His father owned a gym and he was already and accomplished gymnist and boxer. As Nazi persecution against Jews became more prevalent, he began putting together a system of self-defense to teach others so that they could protect themselves from attacks against Nazi youth gangs. Because of the times, he didn't have years to teach people how to defend themselves and the system was developed to be simple and effective. It took instinctive responses (like instinctively raising your hands to your throat if someone is choking you) and turned them into trained responses (like the pluck used in a basic choke defense). It was named Krav Maga (Hebrew for Contact Combat). When Israel was formed, the Israeli military adopted the system for their use. KM relies on a fast, aggressive and decisive counter-attacks to any attack so that when you disengage your attacker isn't going to get up and come back at you a second time.
It's been my opinion that the physical conditioning portion of Krav Maga is vital to the overall system. The minimum level of cardio fitness you should be in is to be able to fight off multiple attackers for at least 90 seconds (for us, that's the average time it takes to get assistance, if you're by yourself then you're going to need longer). That doesn't seem like a lot of time but we run a drill called bull-in-the-ring where the student has to fend off multiple attackers for 90 seconds and it isn't often that I have one of them not be huffing and puffing in the end. I want my people to go home to their families at the end of their shifts so I spend at least 30 minutes of a two hour class working on cardio plus various stress drills throughout to keep me entertained...oh, I mean keep them engaged in the class.
I think the problem with the LA style KM schools is that they try and market KM like you would Tae Bo (or whatever the hell that cardio kickboxing fad was called) with a self-defense element and that waters it down.
I do think that the "aggresiveness" of the counter-attacks in KM is appropriate to the US today. The techniques being taught are used for self-defense, more often then not when someone is using a level of force against you that is intended to cause either great bodily injury or death. As long as you aren't the primary agressor (meaning you didn't start the fight) then in most states, you are well within your rights to defend yourself.
I know some of that was repeat info but I wanted to chime in.