Syntax highlighting is just a tool to eke out a few points of productivity in reading code. I know many people prefer plain text, notepad-style, but some of us like reading typeset documents where formatting (bolding, color, lines) is applied to make the document structure more pronounced.

I think much of it has to do with your attitude toward typography: do you view it as being utterly pointless and devoid of value, or do you like things that don't look like featureless crap.