@TorringtonDean
my point about the weight is that if a plane was made to seat, say 300, passengers all of average weight and that was all it could take then to cram in 360 or whatever would obviously be a danger. But they keep cramming in lots of extra passengers compared to decades ago. So, although there is a maximum weight capacity, it is obviously very much higher. There is also the baggage on top of that.
No, airlines are not just cramming in seats regardless of legal weight limits, it doesn’t work like that.
First issue is that if you are trying to compare 70s with now is it’s different aircraft…for example early marque 737s would have had a much lower maximum allowable take-off weight than a newer model 737…
If you’re looking at changes more recently the builders and the airlines can (sadly) find the weight to cram more seats in by reducing aircraft weight in other areas - e.g. make galleys smaller and lighter..it’s pretty obvious that has gone on if you look at some of the new Airbus NEOs where the galley space and toilet space at the back is tiny.
With the bigger stuff (like the big Long Haul types) carrying say 300 plus it’s not uncommon to see perhaps 300 seats one varient verses say 360 in another, 340 in another, but again you stay below maximum weight for the type by changing the cabin configuration, perhaps taking galleys and toilets out and being aware that sometime you might have to reduce the amount of underfloor cargo that can be carried if all the seats are full…it is all carefully monitored and checked for every single flight….
Fundamentally to go back to your original point extra seats are not being shoe horned into aircraft without any regard to the rules covering issues such as maximum allowable weights….