Asklemmy

Ask them to do so themselves, voluntarily.

If they refuse, the argument stands.

If they accept, you won't convince this person.

You start by giving up on making them understand.

You put the someone in a re-education camp

Let's start with the second part of your question? How do you make someone understand that invading another country is not a good thing?

Issue is that "old people" had to spend their time in the army, sometimes even in a foreign land (Good old time of the colonial war), so kids these day feel so privileged

I mean, we can blame the boomer for a lot of thing, but in the 60's and sometimes 70's (In many countries) young men had no option but do a military service which way involved going to fight to keep the colonies.

War is horrific. If we deem a military is necessary to a peaceful society to protect from threats both domestic and foreign, then we should have a draft of ALL able adults, not just the poor and underprivileged. Rich folks, political folks, and otherwise connected individuals should be subject to be put on the front lines right next to the rest of us. What that means is we might rethink, as a nation, any military action. An all volunteer military would be the next most preferable one that is paid equal or greater to the national average income with full lifetime benefits including healthcare for the whole body including mind, teeth, eyes, etc., pension, free education including masters and doctorate level education, housing, as well as meeting other basic needs of life.

Anything less than that should be unacceptable.

I mean you can look at Russia as an example for how much of the economy was hurt by forcing people out of normal occupation and into service. You also have too look at their abysmal attrition rate to see its unsubstainable and if used primarily leads to worse and worse outcomes on the battle field as they less and less qualified personnel.

Appealing to morality is probably a lost cause for someone supporting a draft, they have already bought into war as a solution. Like moral arguments that Russia is choosing to sacrifice millions and set back their region is something they are already choosing to ignore, forcing people to do it minor in comparison.

I didn't think it's wrong universally, for example, Ukraines current offensive into Russia.

You hold up your draft card and burn it.