YABU, and here's why:
To pay the 40p income tax rate you have to be earning £41,452.
A single person with no children earning £41,452 (£31,142 after tax and NI) has an income higher than 90% of the UK population.
A single person with two children earning £41,452 (£31,142 after tax and NI) has an income higher than higher than 70% of the UK population.
A married couple with one earning £41,452 (£31,142 after tax and NI) and the other the UK median wage of £26,500 (£20,975 after tax and NI) have an income higher than 86% of the UK population.
A married couple with one earning £41,452 (£31,142 after tax and NI) and the other the median wage of a UK shop worker of £11,174 (£10,553 after tax and NI) have an income higher than 71% of the UK population.
Whichever way you look at it, those earning above £41,452 per annum fall into the richest third of society and it's only fair that they pay their way.
(I used The Guardian's income comparison tool and MSE's Income Tax Calculator to calculate these figures).