The majority held that:
The obvious purpose of the statute is to protect existing Government, not from change by peaceable, lawful and constitutional means, but from change by violence, revolution and terrorism. That it is within the power of the Congress to protect the Government of the United States from armed rebellion is a proposition which requires little discussion. Whatever theoretical merit there may be to the argument that there is a "right" to rebellion against dictatorial governments is without force where the existing structure of the government provides for peaceful and orderly change. We reject any principle of governmental helplessness in the face of preparation for revolution, which principle, carried to its logical conclusion, must lead to anarchy. No one could conceive that it is not within the power of Congress to prohibit acts intended to overthrow the Government by force and violence. The question with which we are concerned here is not whether Congress has such power, but whether the means which it has employed conflict with the First and Fifth Amendments to the Constitution.The majority held that the statute did not violate the First or Fifth Amendments because it was directed as "advocacy, not discussion." The Court commented that although Gitlow and Whitney had not been expressly overruled, the view of the dissent had ultimately prevailed -- speech could be forbidden only if it posed a "clear and present danger" of imminent lawless conduct. But it then defined "imminent" extremely broadly where the issue was violent revolution:
Obviously, the words cannot mean that before the Government may act, it must wait until the putsch is about to be executed, the plans have been laid and the signal is awaited. If Government is aware that a group aiming at its overthrow is attempting to indoctrinate its members and to commit them to a course whereby they will strike when the leaders feel the circumstances permit, action by the Government is required. The argument that there is no need for Government to concern itself, for Government is strong, it possesses ample powers to put down a rebellion, it may defeat the revolution with ease needs no answer. For that is not the question. Certainly an attempt to overthrow the Government by force, even though doomed from the outset because of inadequate numbers of power of the revolutionists, is a sufficient evil for Congress to prevent. The damage which such attempts create both physically and politically to a nation makes it impossible to measure the validity in terms of the probability of success, or the immediacy of a successful attempt.It held that the "gravity of the evil, discounted by its improbability" was the formula to apply. Since violent revolution was so great an evil, speech in its favor could be legislated against even if the danger was extremely remote.
Justice Felix Frankfurter issued a concurrence that was effectively a call for judicial restraint, urging the Supreme Court to leave such matters to the legislature. Justice Jackson also concurred, saying that the "clear and present danger" test was fine and good for anarchists and radical socialists who generally engaged in spontaneous and individualistic violence, but that Communists, as a tightly disciplined conspiracy, were too dangerous for the formula to apply, and that stronger measures were needed. He argued that the Communists were guilty of a criminal conspiracy (to overthrow the U.S. government), and that the First Amendment did not protect criminal conspiracies.
Justices Douglas and Black dissented. Black argued that the defendants had not conspired to overthrow the U.S. government or even circulated publications advocating the overthrow of the U.S. government, and that banning organizations that believed in violent revolution was a form of prior restraint. Douglas began:
If this were a case where those who claimed protection under the First Amendment were teaching the techniques of sabotage, the assassination of the President, the filching of documents from public files, the planting of bombs, the art of street warfare, and the like, I would have no doubts. The freedom to speak is not absolute; the teaching of methods of terror and other seditious conduct should be beyond the pale along with obscenity and immorality.But he argued that nothing of the kind had been done, and that the courts were acting as if it had. He went on to argue that the danger posed by the Communist Party was negligible, and that the law could not legitimately treat it as a serious threat.