It's not a "slippery slope" to help all women, even the delusional ones who think they are men. Feminism that excludes males because they aren't female is perfectly reasonable but feminism that excludes females for any reason (including that they are delusional) is not.
It is actually a slippery slope to harming all women who might want to breastfeed at some point in their lives, especially those who have gender confusion.
Widespread use of the words "chest feeding" means less exposure to the concept of breastfeeding. This is likely to further reduce breastfeeding rates, with both women and their male partners finding the whole concept alien.
It feeds into the euphemistic use of the phrase "top surgery" with these women being completely ignorant (in some cases) of the fact that they are signing up to a bilateral mastectomy and loss of the ability to feed their baby should they have one in the future.
Freddy McConnell, the "seahorse dad" who failed to persuade the courts to allow her to be listed as the father of the babies she has given birth to on their birth certificates, is in record as being surprised that she didn't produce any breastmilk and sad that she could not breastfeed.
Yes I am using correct sex pronouns. It is simply not appropriate to do otherwise when discussing birth and breastfeeding.
It also helps men who want to dose themselves with a cocktail of drugs and "feed" a baby the resulting exudate to co-opt breastfeeding for themselves. Because funnily enough when it comes to men, actual MEN, "feeding" a baby, suddenly they are more than happy to discuss their breasts and claim that they are breastfeeding.
Maternal and child health are too important and there is no kindness in polluting language so that no one knows what sex a person feeding their baby is or how they are doing it.