Nothing can erase your physical sex. No matter how much surgery, no matter how many hormones, if your dead body is found skeletal and decayed on a hillside. The pathologist will be able to work out what your sex is regardless of what gender you did or did not live.
You need to be born which female sexual organs to conceive and give birth.
As for chest feeding, men have breasts and presumably with the right hormones could breast feed, where else on the chest could a baby access nutrients? I cannot see any problem with breast feeding.
I do not think the needs and wants of small groups in society should be ignored because they are a minority, but when a minority in society demand major society wide changes that could majorly disadvantage half the population that are not the same as them, there I find myself digging my toes in and saying 'no'