I have been a member of the unorganized militia, being male in reasonable health most of the time, and am no longer in it since I'm over 45. I'm not that fond of guns, and never got training with one. I've never had any sort of military training. Any militia with people like me in it is not going to be "well-regulated". I do want to have all my Constitutional rights, even the ones I don't care about in practice (nobody has ever tried to quarter troops on the homes of anyone I know, for example).
People forget that personal rights come with personal responsibilities, one of which being called to serve in the unorganized militia (if one fits stated criteria to serve, age, etc) and fight in combat if required to do so. It is compulsory. Refusal during wartime (only scenario where the UOM would be activated and this would apply in) could result in immediate execution or imprisonment.
Nobody requires you to own a firearm. However, you may still be called to serve. If nobody has a spare firearm and ammo to lend you, you may find yourself charging a defended position as the 'meatshield'.