I think this is one of those "religious" wars things - although us proportional fonts people are much the minority.
I've used proportional fonts since the early nineties and written thousands and thousands of lines of code since then in a proportional font. I have occasionally tried to go back to a fixed width font but I can't be bothered trying to get past the "it makes my head" hurt stage. (and likewise I can't imagine a lot of fixed width people getting past that stage going in the other direction).
We can rationalise our choices all we like but I doubt that there is any serious advantage or disadvantage in either.
I've used proportional fonts since the early nineties and written thousands and thousands of lines of code since then in a proportional font. I have occasionally tried to go back to a fixed width font but I can't be bothered trying to get past the "it makes my head" hurt stage. (and likewise I can't imagine a lot of fixed width people getting past that stage going in the other direction).
We can rationalise our choices all we like but I doubt that there is any serious advantage or disadvantage in either.