It's going on a billboard in Kentucky. I think it's pretty bold- but then, what from PETA isn't bold? PETA is pushing breastfeeding because if infants are breastfed, they aren't given dairy formula, reducing the number of cows suffering to produce milk.
When I was pregnant and vegan, I was shocked by how many people thought breastfeeding wasn't vegan and assumed I'd give our child soy formula to avoid giving her milk of any kind. People decide to follow a vegan lifestyle for all kinds of reasons- but every one of them that I know of allows, even encourages, breastfeeding your infant. Health reasons would encourage breastfeeding because it's healthier for the infant and the mother to breastfeed. Animal's rights reasons would encourage breastfeeding because no animals are suffering for production or testing of the milk. Environmental reasons support breastfeeding because nothing has a lower carbon footprint than breastfeeding- no production costs (besides mom's increased food intake!), no transportation costs, no energy used to heat the milk.
Not too long ago, PETA tried to reduce cow's milk consumption by comparing it to human breast milk. A letter was written to Ben & Jerry's asking the company to use breast milk. After all, the letter argued, breast milk is intended for human consumption, whereas cow's milk is intended for cow consumption. If we used human milk, we could stop stealing milk from the cows. Interesting logic, but I think coconut milk icecream has a better chance of winning over converts.