Dear Steezie. I can't give you an US perspective, but during the Cold War from about 1960 to 1994, we had National Service (Draft). Let me put it this way - it is not as scary as people make it out to be. The movies make it much more than it really is. here was the South African perspective (Check some of my other posts for more details on this.)
National Servicemen were rated RE health + Psychological as follows:
G1K1 = Can do combat in combat unit, can be far from home (include shipboard for navy)
G3K2 = Secondary roles, yet can also be far from medical centres.
G4K4 = Must stay near medical centre if requiring treatment
G5K5 = cannot be called up
Being G1K1 did not mean that you would be in a combat unit. I was G1K1 and was a medic.
For every combatant, there had to be seven others who were in secondary roles to back him up in the field. So the chances of you being a combatant in a forward position, especially as the US has such a large population is probably very small. (minute!)
There are many things you could do: medic, driver, admin, etc
As call-up/draft was part of law, not arriving for duty would be a criminal offence. National Service was two years plus "camps"(territorial army in UK, National Guard in US?) As far as I can make out no Conscientious Objectors were ever given off. Either they applied for Merchant Navy or Prison services, etc, or they were in Military Prison for THREE years.
Can I say that the war you guys are fighting is similar to the counter-insurgency war that was fought in Angola. This means the following. It's not a case of going in, nailing an objective, the war ends and everybody goes back home. This is something where there will always be enemies lurking in the bush. They will be unseen, part civilian population, striking when nobody expects, joining the side they fear more than the side that is ethically nice.
We could react to this by saying, "Naw, I don't think I like this war," but reality will be that there will be no choice - not because draft would be made law, but because in the end you HAVE TO survive. It will be nasty at times - people back home might at times not support you because it may involve civilians, but they might not even realise that THEIR survival might be at stake.
The question you asked is a serious ethical question - maybe even to the point of VOLUNTEERING or not. I hope this answer helps you.