Awh, I'm so sorry someone made you feel bad. I have reported that question. It's totally unacceptable for ANYONE to make you feel bad about your choice of not breastfeeding!
I'm sure your feelings of guilt have nothing to do with your defensiveness. I'm SURE you gave it your best shot. I find that the women who actually have tried breastfeeding, really tried, longer then 5 minutes, really don't feel guilty. They are completely comfortable with their decision to formula feed and are not bothered at all by breastfeeders. The moms that probably didn't try as hard as they thought they did... once they started talking to breastfeeders and listened to their horror stories about how breastfeeding was so hard for them, but they stuck it out.... they tend to be the defensive ones.
But, you can't tell them that! It's a big secret, hush hush, you don't want to make them feel any worse then they already do!