I never floss, used to. Everytime I did my gums would bleed and I'd spit blood. Now that I don't brush my teeth, I tried flossing today and guess what ? No blood.
What weakens the gums are undesirable bacterial at the gum line that eat gum tissue. My theory is that when you eat right and don't brush, a proper "balance" of good oral flora come into existence, much like "good" intestinal flora. Brushing wipes away the good flora. Liken it to what the condition of the gut would be if one were to brush it twice a day - a bad idea. My gums feel better than ever now that I don't brush, and for the first time in my life I didn't bleed after flossing. Flossing was a pain in the A anyhow, and besides, I never seen any animals flossing. Its probably a good idea for folks who don't know what not to put in their mouths.