Run me through your back of the envelope calculation here. It seems to me like you have plugged in -infinity for the utility of heart disease which is an example of the scale insensitive reason you are currently accusing people of.
You're the one who has taken the stance that people who say "standing is bad for your back" are universally failing to account for the relative scale of the two considerations. I think it's likely that you're making a number of errors yourself when coming to that conclusion, and I would appreciate it if you would share them.