While I agree in theory, in practice airline seats are too small for almost everyone these days. That's not just saying people are larger, but seats and seat pitch, leg room, head room, etc is all shrinking.
I am all for being fair, however it's time the airlines treated customers like people rather than like cattle. If they can sell me more leg room for $40-50 a flight segment, they can afford to set the panes to accommodate some larger passengers without screwing them around.
RNY 5/17/10 highest: 407 lb - maintaining a loss of 200+ pounds and enjoying life