The author of that page did not come to the conclusion "do not use antivirus software because it will make your computer slow" but rather ask consumers to make an educated decision about which software to purchase based on their detection rate.
Malware will also slow down your computer, and could result in your personal information being stolen. If the choice were between waiting an extra few seconds for my computer to boot or having all of my files accessible to people I neither know nor trust, I would choose the former.
"You're doing it wrong" personified right there. If you're using MacAfee or Norton, that's like wrapping a seatbelt around your neck (as those numbers show).
If you're working without at least common-sense anti-virus protection, you're going to deserve what you'll eventually get.
I just kicked Norton of my wife's Vista PC, thanks to Norton's own "Norton Removal Tool".
I'd like to know what your definition of "common-sense anti-virus protection" is, though. Apart from "don't download/install anything from untrusted places".
