Pfft... we don't need compulsory service for the people, we can just turn the local wildlife on them, that'll take care of any intruders
On a serious note, most countries don't need to have compulsory service, and I don't think that forcing military service on people who don't want to or can't do the work will not end well. I can understand the practical applications in some countries like Iran, which are often in conflict for some reason or another or in smaller countries with a lower total population (i.e. not enough to make up a military force based on volunteers alone), but in most Western countries where the militaries can have a decent military size (and a military reserve) based on those who chose that career path, it makes little sense to force everyone to do it.
On a serious note, most countries don't need to have compulsory service, and I don't think that forcing military service on people who don't want to or can't do the work will not end well. I can understand the practical applications in some countries like Iran, which are often in conflict for some reason or another or in smaller countries with a lower total population (i.e. not enough to make up a military force based on volunteers alone), but in most Western countries where the militaries can have a decent military size (and a military reserve) based on those who chose that career path, it makes little sense to force everyone to do it.