Just because manufacturers want lighter weight doesn't mean they have the right to risk our safety for it.
Manufacturers don't want it. You do.
This could get psuedo political.... but....
Most hybrid buyers are liberal - one of their major agendas is increasing CAFE standards to increase fuel mileage. To be "green", whether accurate or perceived. To increase sales of hybrid and electric vehicles and reduce "pollutants".
As a consumer, you don't want to buy the extremely well built/engineered hybrid/electric (Tesla) and/or you can't afford it. As a consumer, you are asking/demanding for higher fuel mileage and lower cost hybrid cars.
Hybrid systems are expensive. In order to meet CAFE standards, hybrid expectations, MPG expectations, AND a cost low enough to the consumer - something has to give.
It's why in a prius all of the interior is made from plastic. They advertise it as green by saying it's all made from recycled material (to make the buyer all warm and fuzzy about the environment) - but the fact of the matter is.... it's cheaper and lighter to make than a traditional thick 'cardboard' with rubber wrapped/leather wrapped add ons and pockets. The seats aren't as nice/comfortable/soft as what may be found in other vehicles - it's cheaper because they have to offset the cost of the hybrid system.
Same goes for the sunroof. If the standard thickness of automotive tempered glass is 3-5mm and - whoah, look at that, we were using 5mm and we can now use 3mm.... saving almost 1/2 the material cost and saving weight.... it's a win win for cost and MPG.
Hybrid battery systems are heavy. Weight offsets need to happen.
It isn't the manufacturers wanting this. It's buyers expecting more for less.
Here are sales figures, in thousands:
2015 43.7 (through July)
so that's a total of 563,200 Prius's sold since 2011, the supposed year where the "manufacturing defect" took place.
Lets go with a low figure and say 20% of the were sold with sunroofs.
So that's 112,640 Prius's sold since 2011 with sunroofs.
Per your claim "hundreds" have complained. Lets say not all are complaining and that's 10% of those who have been "impacted" (no pun intended). So, lets say 5,000.
Not all who have complained by any means are Prius, especially since there was a recall of aftermarket glass in the US - so lets say 25% (which is an exaggeration) are Prius's.
So, that puts the "defect" at about 1,250 cars.
That is literally 1% of the Prius vehicles with a sunroof sold since 2011. A 1% failure rate is not a manufacturing defect.
We are also talking about many that are 5 years old at this point. Since we are talking about glass here (which is an easily broken item - how often are you chucking little pebbles at the windows of your house and angry when they break?).... a 1% "failure" or really, replacement, rate.... is probably considered not bad at all.
Now you call yourself "Last Toyota" but really, if you were intelligent - it would be "Last Sunroof".... because Toyota has nothing to do with it. Every make/model someone online is complaining about their sunroof "exploding".
Lastly - if you were to go buy a car and they said "Well, the sunroofs are made thinner to save weight and costs.... We have a solution to make them less likely to burst - we've seen reports of about 1% have broken while driving. We offer a specialized film layer that can be added for an addition $750, and then we also offer a monthly insurance - so that if your sunroof were ever to burst, we would replace it. The replacement cost is usually $1500-2000, so the cost to replace isn't cheap. The monthly cost is an additional $15."
Would you buy the film and insurance?
Or would you brain go "99% chance it won't happen to me, $750 extra up front and an additional $900 over the course of 5 years is actually more expensive than a replacement cost... so, no I will not buy the 'extra protection'."