I am what some of you impolitely term a lard arse. But then I don't get on an aeroplane and turn right. I have enough air miles not to have to sit down the back with the impolite so-and-sos posting here on my personal trips. 'The Company' pays for me to travel J-class for business purposes. So should I have to buy a second J- or F-class seat, too? What use would that be, given that most are 'podded' these days? And that I don't spill out of my own seat anyway. Honestly, the attitude of some here is disgusting.
As for the MZFW argument - well, when travelling as a family I travel with my svelte wife (60kg or less) and my 3 year-old (about 13kg), so I wonder how we average out? Around 60kg, I suppose.