Why does Hester feel that the reverend and the magistrates cannot take the scarlet letter from her breast?
In addition to being liberating, the scarlet A becomes a badge of defiance and transgression. It has enabled her to become an "other" in her community, which is deeply judgmental, and in separating herself from it she develops an identity apart from the people in it, and this new identity in many way is more moral, embraces more goodness. Separated, too, she is able to raise Pearl to be other than what the child would be if living in that deeply judgmental community. In a sense, then, the A empowers her to continue to resist the dominant ideology that her act with Dimmesdale initiated. Everything about Pearl is Hawthorne's way of approving of that resistance and disapproving of that ideology.
The scarlet A is first meant for Hester to be a reminder to everyone of how they should behave. Over the years, however, the scarlet A becomes liberating for Hester because it allows her to do whatever she can to help others and to get involved in the community. Having worn the letter for so long, it has now become a part of who she is, and she can't imagine not wearing it. It has become her badge of honor and is an extension of who she is.