We are very lucky to live at a time when infant formula has been developed that enables babies to thrive and develop as well as those that are breastfed. Of course babies who are bottle fed will grow up to be healthy when in the past they may have struggled to survive on the alternatives available. I do not think mothers who bottle feed for any reason need to feel guilty in any way. That doesn't mean that breast milk is not the ideal; of course it is, just as cows' milk is best for calves, mares' milk is best for foals, bitches' milk is best for puppies etc etc, and more should be done to support new mothers with breastfeeding.
All that said, there has always been pressure and disapproval about the way babies are fed. When I had my children in the 1980s there was definitely pressure to breastfeed and disapproval from some quarters towards those who bottle fed. This was the era of the NCT and LaLeche League. Before that, from the 1950s onwards I believe mothers were pressurised into bottle feeding; as someone said earlier this initially had a lot to do with getting mothers back to work. So I don't think the pressures today are new, but what is different is the rise of social media. Young people now are bombarded with messages that say everyone else has the perfect body, perfect family, perfect baby, perfect partner, perfect home, perfect holidays, perfect everything. I think this is where the difference lies and it takes a strong woman (or man) to remain unaffected by it.