The usual advice for anyone who is concerned about legal trouble with the U.S. government in the future is to get a lawyer.

Since there people, all the way up to U.S Presidents, who have been excused from conscription for all sorts of reasons, I suspected that there are lawyers who are aware that some people do not want to be drafted for a variety of reasons. They could also give you things like rates, which would help in any cost benefit analysis.

For instance, here is a link to a lawyer who specializes in a type of Conscientious Objector law that I found through googling:

http://jameshfeldman.com/discharges_for_military_conscientous_objectors.html

It appears that this particular person focuses on discharges for people who are already in the military. But it seems likely that he might at least point you in the direction of other resources.