What if the US had mandatory military service?

The countries that have mandatory military service are those that have severe tensions with the countries next to them. For example there's Switzerland, Israel, South Korea, North Korea, and Taiwan. The huge downside is that the country can go full on nationalism like Hitler or the Spartans. But what if the country remained rational? In my opinion South Koreans and Taiwanese are pretty cool people. I know enough of their pop culture to see that they are happy and loving people. I really don't see any fascism popping up in either of those two countries.

I bring this up because although there are possible downsides, I think there's plenty of upside. There are three specific examples that come to my mind. 1) For one the amount of overweight and obese people will go down tremendously. Even though people won't be as fit after they leave the military, a two year service is enough to instill the right mindset to live healthily for life. 2) This can also reduce gang violence. Sure a huge downside is that some gangsters will return back to their gang with the ability to shoot straight, but many more gangsters will probably have their life turned around. After all, gangsters are soldiers at heart, they just want to find somewhere they belong. Military service can instill duty and morality. Many former gangsters will return as good citizens. 3) America will be less likely to go to war. It's easy now to let Congress vote to go to war, but what if all families had sons and nephews in the military? Do you think Congress would be on shorter leash? Hell yeah. The Iraq invasion probably would never have happened.

I was just curious about the idea, I don't have an opinion of whether I'm even in favor, I'm just saying there are definitely good consequences of such a system. The thing that made me interested is the Swiss model. They have mandatory service starting at 20 for one year and they are part of the military reserve until age 30. and are part of the reserve reserve until 50. While in reserve service they are each assigned an automatic SIG assault rifle which they keep in their own homes! Compare that to American soldiers, who cannot even keep sidearms with them while they are on BASE, (that's how the Fort Hood shooting was able to happen).

But I realize what works for one country won't always work as well for another country. What are your opinions on a mandatory military service?