Under a DICKtatorship, the government tells you you WILL join the military, and you can't say "no".
Under a DEMONcracy, the government will condition you into "voluntarily" joining the military, whether through the schools (government indoctrination centers), mainstream media (propaganda rags), fun ads (hehe, look at this mess we created in Ukraina, it's almost like real life Call of Duty right?), monetary insentives (get massive tax cuts by shooting innocent Muslims!), or fines (if you won't join, you'll get fined with rates going up every year you're not in the military).