The ruling of the court was 6-3 with 3 of the Justices dissenting.
Justice Roberts dissenting, “I dissent, because I think the indisputable facts exhibit a clear violation of Constitutional rights.
This is not a case of keeping people off the streets at night as was Hirabayashi v. United States, nor a case of temporary exclusion of a citizen from an area for his own safety or that of the community, nor a case of offering him an opportunity to go temporarily out of an area where his presence might cause danger to himself or to his fellows. On the contrary, it is the case of convicting a citizen as a punishment for not submitting to imprisonment in a concentration camp, based on his ancestry, and solely because of his ancestry, without evidence or inquiry concerning his loyalty and good disposition towards the United States. If this be a correct statement of the facts disclosed by this record, and facts of which we take judicial notice, I need hardly labor the conclusion that Constitutional rights have been violated.”( http://www.law.umkc.edu/faculty/projects/ftrials/conlaw/korematsu.html)
Justice Murphy found the case brought to the court fall into racism. Continuing his dissent he further stated, “In dealing with matters relating to the prosecution and progress of a war, we must accord great respect and consideration to the judgments of the military authorities who are on the scene and who have full knowledge of the military facts. The scope of their discretion must, as a matter of necessity and common sense, be wide. And their judgments ought not to be overruled lightly by those whose training and duties ill-equip them to deal intelligently with matters so vital to the physical security of the nation.
At the same time, however, it is essential that there be definite limits to military discretion, especially where martial law has not been declared. Individuals must not be left impoverished of their constitutional rights on a plea of military necessity that has neither substance nor support. Thus, like other claims conflicting with the asserted constitutional rights of the individual, the military claim must subject itself to the judicial process of having its reasonableness determined and its conflicts with other interests reconciled. "What are the allowable limits of military discretion, and whether or not they have been overstepped in a particular case, are judicial questions." (http://www.law.umkc.edu/faculty/projects/ftrials/conlaw/korematsu.html)
Justice Jackson dissenting, ”Korematsu was born on our soil, of parents born in Japan. The Constitution makes him a citizen of the United States by nativity and a citizen of California by residence. No claim is made that he is not loyal to this country. There is no suggestion that apart from the matter involved here he is not law-abiding and well disposed. Korematsu, however, has been convicted of an act not commonly a crime. It consists merely of being present in the state whereof he is a citizen, near the place where he was born, and where all his life he has lived.
Even more unusual is the series of military orders which made this conduct a crime. They forbid such a one to remain, and they also forbid him to leave. They were so drawn that the only way Korematsu could avoid violation was to give himself up to the military authority. This meant submission to custody, examination, and transportation out of the territory, to be followed by indeterminate confinement in detention camps.”(http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=US&vol=323&invol=214)