Three things:
1. If a fresh novice is on GSLP, they're going to be on so low a weight starting out that max reps for the last set isn't going to be that big of a deal, bad form or not.
2. Even if they were doing so many reps for their last set that their form deteriorated to shit, which it shouldn't because the novice would be at a light weight, it would still be after two sets of five. If they're messing up on the third set, there's an issue with form to begin with, it's not due to the extra reps as they would have had two sets of five to begin with.
3. GSLP's progression is 2.5lbs-5lbs jump for upper body movements and 5lbs-10lbs jump for lower body movements. No novice is going to do five reps on Monday and then, come Friday, that 2.5-5lb jump is going to be their max to where they're doing shit form to get the rep up.
To each their own, though. I find the concept of having two PRs per sessions, a weight PR and a volume PR, allows for more goal setting and removes the reset as a discouragement since going back to an older weight allows the trainee to now beat their previous volume PR. That type of PR breaking on a novice is incredibly inspiring and self motivating.