I forgot one of my main points in my list of problems with the system of girls not learning Gemara:
4)There is no goal within Judaism for girls to strive for. Once they come back from seminary it’s basically over. They spend the rest of their lives helping other people accomplish things but never have a chance to accomplish something real themselves. For some, this can be very disenchanting. Boys on the other hand, constantly have something to aspire to – mastering the ever growing corpus of shas and poskim. Every masechta they finish is a real accomplishment. Girls won’t ever really get that feeling.
On a similar note, when girls need something to do they have very few options and will often end up wasting a day watching movies or something. If they learned Gemara, they would always have something to do. (Obviously this doesn’t mean that they would use all their spare time to learn; it means that in the overall scheme of things they will spend more time learning and less time doing things that can get them into trouble.)