It was in this case. Some worlds and regiments forcibly conscript, but most are voluntary. Propaganda is a great thing. Volunteers have higher morale, greater discipline and greater resolve. And are also less traitorous and/or susceptible to Chaos's influence.
Look at this, for example. Had it been forced conscription the Guardsman would've shot the wounded one where he lay and pilfered his gear. There's an integrity to be had with voluntary regiments.
Does a life of danger, glory and service to the Emperor tempt you? You get great pay which you can spend any-Emperor-damned-where you please, you get to wear the Imperial Aquila, which basically tells any local yokels to not **** with you unless they want the Arbites or your buddies to come calling (whichever arrives first, we're not picky) and by serving the Emperor and putting lasbolts into the faces of enemies of the Imperium, you accomplish a hundred times more than what some dusty-arsed old Ecclesiarch can hope to achieve by droning on and on about **** you know already.
Sure, the life isn't exactly fun. Neither will you be ever entirely safe, unless you happen to sign up with one of the pansy-face parade ground regiments. But you know how the saying goes - no inspection ready force was ever ready for combat, and no combat ready force was ever ready for inspection.
You ought've learned the basics at the PDF training facilities already. All it takes now is a 10% luck, 20% skill, 15% concentrated power of will, 5% pleasure, 50% pain, and they'll have 100% reason to remember your name.
Should you end up in the **** and should you survive, you'll end up near goddamn unkillable. The Imperium takes care of its heroes well.
For the meantime... well. Look at this ************ . Are you a bad enough dude to serve the Emperor?