before giving a gun to a criminal, wouldn't it be wiser to conscript the civilian?
i mean, if the problem is freeing the prisons, death sentence immediately and with no stops to all demonstrated homicides and pedophiles, a clear distinction. the morality or ethicity of the thing is secondary, a problem is not ethic or moral, a problem is a problem. One must apply the best solution to solve it.
War is a problem. A murderer is Not someone trained to war, not only that, he is mentally unstable. You will be giving to him assault weaponry capable of tearing a human in half with three bullets, not only that, but you'll need to train them in the art of the soldier, unless you wish to use them as meat shields, in which case you just free them naked on mined camps and see how many mines they blow up before dying. Or use their corpses as sandbags.
On the other hand, a civilian might feel a tad despaired being conscripted and all, but a little bit of brainwashing "you'll be fine, were sending you conscripts to an easy zone, filled with !!FUN!! and to relief the military" would certainly calm them down, and they'd go through training. Obviously.
Point is, war fought with penal legions poses two problems: training criminals who will likely use whatever they can to ditch/Escape/keep the shiny weapons for personal usage and making sure they do not rebel at the beginning. i mean, a criminal would rather say "NO i stay all my life in prison with my sentence, i get food, a bed, clothes, and get all the rape i want" then "let's go and get shot down by god-knows who doing god-knows what." if they don't train, their useless, unless as said before you want meat shields, but you'd still spend gasoline bringing them to the front and food and beverage until they are actually shot, so wouldn't it be better to just kill them with an axe and bring their corpses?