Yup I have always wondered what it was like back in the 1960s when the first women started to wear jeans. Obvioulsy they were bucking the trend and would have been stared at as well, but I have never heard of any cases of physical attacks etc. Clearly the husbands and boyfriends of these women did not forbid them from wearing jeans in public either otherwise they would have been closeted just as we are today.
You hit the nail on the head Joanie, by saying a woman in jeans is non-threatening. That is the key. It is the old double standard that woman are not sexual beings and thus when they wear masculine clothes it cannot be for sexual reasons.
On the otherhand nobody believes that if a man wears feminine clothing it can be anything else but for sexual reasons i.e. he is a pervert, deviant, homosexual, child molester etc. Anything negative or "evil" is always attributed to men when we deviate from the macho script we are all supposed to religiously follow while women are thought of as saints and thus their reasons for deviating from their script such as crossdressing is never considered threatening.
So women are allowed to crossdress because nobody is offended as women's reasons must be innocent - i.e. it is only done for comfort etc. Nobody wants to think that maybe some women crossdress because they want to, because they like the masculine look, because it allows them to access masculine behaviour and feelings, because it makes it easier to compete against men, because they feel empowered in masculine clothes while they feel vulnerable in femining clothes etc. In fact, there are lots of reasons why women crossdress just as there are lots of reasons why men crossdress.