> This protects against coups, ensures your power in society and prevents groups of officers and soldiers etc. from taking over.
Meanwhile Spain suffered an attempted coup in 1981 [0] while mandatory military service was still in place [1]. The conscripts did not play a role in protecting democracy.
[0] https://en.m.wikipedia.org/wiki/1981_Spanish_coup_attempt
[1] https://en.m.wikipedia.org/wiki/Military_Service_(Spain)
There are no silver bullets. It's just that having (solely) an elite warrior class is an extra risk.
Decision-making in the armed forces is always performed by a "warrior class". The people who operate heavy war machinery are also career soldiers; conscripts are light infantry.
And there is a very real economic cost to mandatory military service. It only makes sense in the context of a small country (in terms of population) bordering a large aggressive neighbor, such as Finland or (possibly) Canada.
No, conscripts operate also tanks and artillery. They also load and prepare combat aircraft.
Artillery and tanks will have some kind of professional officer though.
Armed forces culture is also incredibly important. Goal/mission oriented organizations are harder to co-opt than top-down command structure organizations.