cross posts galore - noseynoonoo, your post is really pertinent - EVERY mother I know who got into genuine problems with supply bf-ing fed formula very early on. The 'go on, just give them a bottle of formula at bedtime, I do, everyone else does' attitude around here is endemic.
I think if mothers CHOOSE to feed formula early on knowing it is very likely to affect their supply, and might lead to the end of bf-ing quickly, then that's one thing. Someone else feeding formula and not realising it could cause them problems is something else.
btw, I know a few women who found bf-ing overwhelming in the early days (being constantly on demand, feeding a lot at night etc) and having fed a few bottles, realised that it gave them a break and they could leave the baby with other people etc - and so they stopped bf-ing.
I think they might have felt better in the long run if they had got through those tough early days (cos it generally does get easier!) - but it's also possible/likely that actually, what they did, for them, was fine and the best thing when you look at the whole picture. Which I never knew, although I was close to them. I bf-ed 100 percent, but always said that if the sleep deprivation got so hellish (it was pretty bad) and I either felt I was heading for depression or a breakdown, I would think again and try formula.
I didn't have to but still think that was reasonable as an approach.