You can't have a country that doesn't have conscription in time of war. For example if Russia were to attack which is unlikely but plausible. I don't like conscription at all and it's necessary but still an evil.
There's a very cold-blooded but good reason why a nation rationally should use men as cannon fodder before women: they are more expendable in terms of reproduction. You need fewer men relative to women. Also, societies with more men than women tend to be unstable and high-crime and whatnot. Societies with more women than men survive a bit better.
It is not necessary, because the state has a legitimate right to taxation. Every non-military person in the country can be taxed down to the poverty level to pay volunteer troops. This is morally superior to enslaving people.
