i hate this whole train of thinking.
should people who go on the pill pay extra taxes because they're more at risk of cancer?
should people who engage in dangerous sports pay extra taxes because they're more at risk of broken limbs?
should people who get pregnant pay extra taxes because giving birth is a cost to the NHS?
where exactly would you like to draw the line?
edit: as i was a bit slow off the mark i'll go ahead and say no, I don't think there should be a 'fat tax'