I honestly believe that the North Carolina bathroom law regarding non-unisex bathrooms and the birth certificate of individuals' sex is not needed. I also think that Target is too gullible with the gender identity thing. Gender is only for pronouns, NOT people. Transgender DOES NOT exist, but Transsexual aka Twin Soul does. If you wish to use the bathroom other than the sex of that which you were born with, get a sex change, then do so.
The problem was Charlotte passed an ordinance requiring all businesses to accede to the LGBT definition of gender for facility use. The state stepped in to return the decision back to the property owners (which is the right place, IMO). If Target wants to let men in the women's room, so be it. It's their bathroom and their customers.