The previous post touched on halachic particulars, but I think the topic of teaching girls halacha also calls attention to sociological biases. My wife touched on this in a recent post of hers regarding what makes some things frum and others not. Our shared assumption is that halacha demands the same meticulousness in observance from women as it does from men (in those areas that women are obligated in), but reality seems to prove otherwise.
The approach of beni torah in the yeshiva world (esp. in recent years) is to try to be “yotzei kol hadeyos” in halacha. That doesn’t mean where circumstances warrant one cannot rely on ikar ha’din or kulos, but no one would suggest institutionalizing these heterim as ideals to aspire to or a baseline of observance.
However, when it comes to women's and girls' observance, the situation is very different. From tefilah to shabbos makeup, somehow it is OK to teach as an ideal a level of observance that falls far short of what yeshiva educated men would aspire to themselves. Somehow the approach shifts from being “yotzei kol hadeyos” to “let’s look for an out”. Somehow the "ben Torah" who won't carry in an eiruv has no problem with his wife pushing the baby stroller down the street on Shabbos.
At the risk of being overly harsh, most women have never been educated to think independently about halacha and growth in observance, and most men care more about what's for dinner than whether their wife is keeping or knows a chumra of the chazon ish. Shouldn't we be striving for higher ideals than that?