There are ways on the user's end to combat some of these: for font issues, adjust them in your browser and don't let web pages change them. Turn on "Large CODE fonts" in your user settings on PM.
in reply to Code Tags
For the "d/l code" option, however, any extraneous stuff in <code> tags without providing for it (ie, use "__END__" on the real code to ease things) is a real problem.
Personally, I find that both serif fonts and proportional fonts make it unappealing to my eyes to read the text. Of course, "Courier New," as a fixed serif font, is rather ugly on the eyes, especially when small. So, I ditch Courier in favour of Andale Mono or Lucida Typewriter for fixed fonts, and Lucida Sans for proportional fonts. Much easier to read.
Closer to the subject at hand, I feel that editing nodes that use the code tags in violation of their spirit is justified, though I would hope that the person doing the editing is the author.
Me spell chucker work grate. Knead grandma chicken.