This is not just an opinion issue, it's one of readability. Good typographic fonts--not monospaced typewriter fonts--are designed with maximum readability in mind.

It's the same reason YOU DON'T WRITE LONG SECTIONS OF TEXT IN ALL CAPITAL LETTERS: YOUR EYES MOVE SLOWLY OVER THE TEXT BECAUSE IT'S HARDER TO RECOGNIZE THE INDIVIDUAL LETTERS WHEN THEY ALL TAKE UP THE SAME AMOUNT OF SPACE. (Well, that and the 'Net-savvy community equates it with yelling!)