Breastfeeding is promoted and very well-supported in the area of Canada I live in, but when I had supply issues, the breastfeeding clinic I went to with my first son had us supplement him with concentrated formula to get his weight back up. No guilt, no problems, just support and good scientific explanations of why we needed to do that.
Yeah, I did feel pretty guilty and frustrated and miserable about the whole situation, but those were my feelings. No one made me feel inadequate.
If anything, our lactation consultants are overenthusiastic to help. As in, they give you about 20 things to try, then call you back twelve hours later to see if you've noticed a difference, and so on. It was almost too much at times.
But when I explained to other health care people about combi-feeding, no one batted an eyelash. Neither did any mum I've come across. I got sympathy, suggestions, commiseration on the outrageous cost of formula, but I don't remember ever feeling judged.
I haven't ever joined any parenting forums that are North American-based, so I suppose that it's very possible that there could be a big divide, but I haven't really experienced it in real life.