-A not insignificant benefit is derived from removing young men from the general population and subjecting them to military discipline (civil defence and police conscripts are subjected to the same disciplinary rules). The 10-15% of bored young men who would otherwise participate in gang activities are removed from their peers while gang leadership succession is seriously disrupted.
Note: Internationally, organised crime is generally paternalistic and male chauvinistic. Since most join for the sex and drugs. And women do not need to look for sex and can exchange sex for drugs.
See other answer on Do countries with Military conscription have lower crime rates?
-well educated liberals would be diverted from organising idealistic social change (Occupy Central with Love and Peace) to more practical "help the disadvantaged" programs such as free tuition and food drives. Since well educated liberals would have been cocooned their whole lives, exposure to different segments of society at that age would be an eye opener. Even if they go through the officers course with most of their peers, they would eventually need to interact with others once they get their command.
And you need universal male conscription of more than a year, ideally at least 18 months to achieve advantages in points 1 and 2.
Why do we not get the women to participate? They generally do not contribute the problems in points 1 and 2.