it's totally acceptable for a woman to wear masculine clothing but not for a man to wear feminine clothing.
I'm struggling for the correct words to express this, so bear with me:
Though women have come a LONG way since the days of not being allowed to vote and the attitudes that a woman's place is "barefoot, pregnant and in the kitchen" we are *still* not viewed as *equal* by the majority.
Therefore, when a woman appears as masculine it's viewed as aspiring to climb that ladder of social equality, not actually to *be* a man, but to show the world they can do most anything a man can do.
On the other hand, when a man appears as feminine it's viewed as him taking a step back *down* that ladder of social equality.
As wrong as the concept has been proven to be, women are still viewed as the "weaker sex".
I do not in any way personally subscribe to, or agree with, these points of view, but I do feel it is a major reason for society's rejection of M2F crossdressers.