I actually didn't see it from patriotic perspective, more like how to absorb HK into China politically. China promised HK 50 years of autonomy, but that doesn't mean China shouldn't do anything until that time came. Letting HKers joining the PLA might be a good way to speed up the absorbtion. But you brought up interesting point about priveleges and benefits. China and HK have different systems and probably level too. Unless those can be bridged, it could create a gap and jealousy and conflict.

For most developing countries, like india, joining the army meant stable career and income, plus there is certain amount of pride. They tend to think the soldiers as above ordinary citizens. like they are special class of citizens. Even worse, the Hindu also have warrior caste, although indian army isn't based on caste, but caste play a big factor in indian psychology, that might even worsen the perception that soldiers are above ordinary citizens. So no surprise many want to join the military. I think it is different in Confucian countries who disdain warfare.