What is a hipster? Look at this fucking hipster...

It's amazing how people often struggle with this simple concept (unless they're trolling :) ). The reason why vegans object to consumption of animal products is because they are generally taken from animals by force and/or violence and against their will (obviously, some people will want to deny that animals have a will that could be broken in this way, and consequentialists tend to have another argument altogether).

By contrast, human mothers, who wish to nurture their babies, more often than not give their milk to the baby willingly. Some can't for various reasons, e.g. they may not have milk following a birth, etc., and it would, of course, also be wrong to take a woman's milk from her by force if she was unwilling to give it. Neither wet-nursing nor milk banks present any problem, though. The milk is given willingly, and that's fine.