In the Dennis et al. v. United States case of 1965, the Supreme Court upheld the convictions of several Communist Party leaders for conspiring to teach and advocate overthrowing or destroying the U.S government by force and violence, a violation under The Smith Act. The defendants argued that their First Amendment rights were being violated as they had not acted upon these beliefs nor incited others to do so immediately. However, in a landmark decision, Justice Hugo Black stated that while abstract teaching of Marxist doctrine was protected under free speech laws, active plotting against the government was not. He further clarified that even if there is no immediate danger from such activities but has substantial potential for harm in future then it can be restricted constitutionally.

The dissenting opinion in the case of Dennis et al. v. United States argued that the majority's decision was a dangerous departure from established principles of free speech and association protected by the First Amendment. The dissenters contended that there was no clear evidence to suggest an imminent danger posed by the defendants' advocacy for overthrowing government, which they believed should be a necessary condition for criminalizing such activities under Smith Act prosecutions. They also pointed out inconsistencies in applying 'clear and present danger' test, suggesting it had been used arbitrarily to suppress unpopular views rather than genuine threats to national security. Furthermore, they expressed concerns about potential misuse of conspiracy laws as tools of political repression, arguing that mere membership or affiliation with organizations advocating revolutionary ideas shouldn't automatically imply participation in any alleged conspiracies to commit illegal acts.