Bottom line, once "you join" you have signed a legal contract. Failure to complete your end of the contract can lead to prison. On the other side of the coin if you can make your case there are certain specific, regulatory avenues (which can be very difficult to follow) where you can apply for a discharge (without receiving benefits of course). I strongly suggest, if you have not signed up yet find and talk to some new recruits recently enlisted and who completed basic training before you make any decisions.
Once you raise your hand in the oath before they ship you off. You're in for whatever the contract called for. You can try for discharges but certain types of discharges will hurt you in life. Keep your part of the bargain.