Edit: removing my summaries.
Asking a question again is O.K. Pointers to discussions here are intended to start discussion, not to discourage follow-on questions, information, or debate.
As an aside for anyone looking for this issue in the future: the search terms "draft" or "conscription" did not work well for me. "Executive Order 9279" worked much better for me, using the Google search phrase:
"Executive Order 9279" inurl:reddit.com/r/AskHistorians
"In WW2 did Marines get drafted?" at https://www.reddit.com/r/AskHistorians/comments/3en1xr/in_ww2_did_marines_get_drafted/ from /u/Georgy_K_Zhukov .
"In World War II, did voluntary American soldiers stigmatize those who were drafted into military service?" at https://www.reddit.com/r/AskHistorians/comments/5h7jdl/in_world_war_ii_did_voluntary_american_soldiers/ . Georgy_K_Zhukov here too, but also /u/staples11 , bug-hunter , and /u/the_howling_cow (flaired in United States Army in WWII) commented.
"During WW2, did the majority of US soldiers willingly enlist or were conscripted?" at https://www.reddit.com/r/AskHistorians/comments/4bzpsi/during_ww2_did_the_majority_of_us_soldiers/ , the_howling_cow again.
Also from the_howling_cow: "Question about military service on World War II" at https://www.reddit.com/r/AskHistorians/comments/5eqeob/question_about_military_service_on_world_war_ii/