Who are conscientious objectors?

Broadly speaking, conscientious objectors are those who refuse to perform a legal duty by reason of religion freedom. However, specifically, the term applies to those who refuse to perform military service"on the grounds of freedom of thought, conscience, or religion.

WIKIPEDIA: A conscientious objector is an "individual who has claimed the right to refuse to perform military service"on the grounds of freedom of thought, conscience, or religion. In some countries, conscientious objectors are assigned to an alternative civilian service as a substitute for conscription or military service. Some conscientious objectors consider themselves pacifist, non-interventionist, non-resistant, non-aggressionist, anti-imperialist or antimilitarist. https://en.wikipedia.org/wiki/Conscientious_objector
GERONA DOCTRINE: In United States vs. Macintosh, 283 U.S. 605, 75 L. ed. 1302, 51 S. Ct. 570, a later naturalization case, the applicant was unwilling, because of conscientious objections, to take unqualifiedly the statutory oath of allegiance which contains this statement: "That he will support and defend the constitution and laws of the United States against all enemies, foreign and domestic, and bear true faith and allegiance to the same." U.S.C. title 8, Sec. 381. His petition stated that he was willing if necessary to take up arms in defense of this country, "but I should want to be free to judge of the necessity." In amplification he said: "I do not undertake to support "my country, right or wrong" in any dispute which may arise, and I am not willing to poromise beforehand, and without knowing the cause for which my country may go to war, either that I will or that I will not "take up arms in defense of this country," however "necessary" the war may seem to be to the government of the day."

The opinion of this court quotes from petitioner's brief a statement to the effect that it is a fixed principle of our Constitution, zealously guarded by our laws, that a citizen cannot be forced and need not bear arms in a war if he has conscientious religious scruples against doing so." And, referring to that part of the argument in behalf of the applicant this court said (p. 623): "This, if it means what it seems to say, is an astonishing statement. Of course, there is no such principle of the Constitution, fixed or otherwise. The conscientious objector is relieved from the obligation to bear arms in obedience to no constitutional provision, express or implied; but because, and only because, it has accorded with the policy of Congress thus to relieve him . . . The previlege of the native-born conscientious objector to avoid bearing arms comes not from the Constitution but from the acts of Congress. That body may grant or withhold the exemption as in its wisdom it sees fit; and if it be withheld, the native-born conscientious objector cannot successfully assert the privilege. No other conclusion is compatible with the well-nigh limitless extent of the war power as above illustrated, which include by necessary implication, the power, inthe last extremity, to compel armed serviced of any citizen in the land, without regard to his objections or his views in respect of the justice or morality of the particular war or of war in general. In Jacobson v. Massachusetts, 197 U.S. 11, 29, 49 L. ed. 643, 651, 25 S. Ct. 358, 3 Ann. Cas, 765, this Court (upholding a state compulsory vaccination law) speaking of the liberties guaranteed to the individual by the Fourteenth Amendment, said: "... and yet he may be compelled, by force if need be, against his will and without regard to his personal wishes or his pecuniary intersts, or even his religious or political convictions, to take his place in the ranks of the army of his country and risk the chance of being shot down in its defense. (G.R. No. L-13954; August 12, 1959)