When I was in the 18-34 age bracket, I didn't really care who stood up where, largely because (a) I could stand up for the whole game; (b) it wasn't a huge hardship on my dad, who was in his 50s and in good shape; and © I didn't have kids whose views were blocked by standers.
At 41, honestly, (a) I don't feel like standing for three hours when I paid good money for a seat; (b) my dad is pushing 70 and definitely shouldn't have to stand up for three hours; and © my kids have a hard enough time seeing over people sitting in front of them without having to deal with standers.
So I've seen both sides of it and I truly believe there is a middle ground. There's a time for standing. The whole game is not it.