The best argument for conscription is that, like politics or the police, the psychology predisposed to choosing it is not necessarily the most beneficial to be involved with it.
If you could choose to serve only in natural disaster relief, humanitarian, or aid operations it would make it significantly less conflicting.
Ultimately the requirement to be involved with, and potentially murder, in anti-democratic or anti-humanitarian operations, and acts of aggression, that could have been decided entirely by self-serving corporate or political interests makes conscription a dealbreaker.