I don't care if someone does it in public, but I think it's polite to make some effort to cover up a little.
There are tons of lightweight, inexpensive breastfeeding covers available, or even the option of just shielding the baby with your arm/shirt..
I was on the bus the other day, and a women kept trying to sell me meat. Not really sure what was going on there, she seemed a little stoned, disturbingly. Anyway, she lifted her shirt up out of nowhere and pulled out a baby from under it. I saw a lot, and I wish she would have tried to remove the baby without flashing a complete stranger.
I don't plan on breastfeeding at all if I even have children, but that's because it's a slight anxiety of mine. I think mothers should be able to breastfeed wherever they want! I just appreciate a teeny bit of effort in covering the important bits.
If there's an accidental flash, hey, that's life, I just appreciate the effort.