I'm not a fan of SL, but from what I recall, it's not true that you are starting ultra heavy on day one. If I remember correctly, you're actually starting with the bar (except for deadlifts).
The bigger problem, IMO, with SL is that when you fail, and of course you will, there's nothing to help you break through it.
Sure, but when you are starting out: The olympic bar - 20 kg, maybe your 5RM and if you have never squatted before and hit your 5 RM on your first day of working out, the probability of injury is more than it isn't.
And what you said is also right; from the page:
> 5×5 means you do five sets of five reps with the same weight. Squat 20kg five times, rack the weight, and rest 90 seconds. Then Squat 20kg for five reps again. Repeat until you’ve done five sets of five (5×5). Then move to the next exercise.
There's no way you can keep the weight same across 5 sets unless, according to the example, 20 kg is your 10RM+ weight. That too with 90 seconds rest. Squats and Deadlifts will gas you out completely. It'll take you 90 seconds to just catch up with your breath. And some more for the actual muscle (and synergists) to recover.
But if you don't get all 5x5 then you keep the same weight for the next workout. An adult male should be able to squat 45lbs for at least a set of 5. They might not hit all 25 day 1, but they have to start somewhere.
The bigger problem, IMO, with SL is that when you fail, and of course you will, there's nothing to help you break through it.