Supreme Court Justices can disagree with the prevailing opinion. This can be viewed as failure to sway the general opinion of the court, but in the end, it can become law. Dissent of the court is often used by presidents or Congress when formulating laws, and often, these dissents are the basis for how the law is formed.
Several points throughout history, dissent has led to future change. In 1896, the Court handed down a 7 to 1 ruling in the case of Plessy v. Ferguson, ruling that separate is equal. The dissenting opinion, written by John Marshall Harlan, was later used by the court for the basis for the opinion in the case of Brown v. Board of Education, stating that separate can never be equal.
Dissenting opinions can also sway the justices, and they can split the court, permitting for more discussion and debate over heated issues. On several occasions, such justices as Ruth Bader Ginsberg wrote dissenting opinions which then become the prevailing opinion thanks to garnered support.
Dissenting opinions also provide precedence for future arguments. In 2007-8, District of Columbia v. Heller, the dissenting opinion created a different definition of the second amendment right to bear arms. Such a definition may be used in future discussions to give backing to opinions.
Dissent, while not necessarily an immediate success, will normally be useful for future discussion, and at some point, that dissent may be viewed positively as the basis for successful changes and laws. Dissent at a time can provide the groundwork for future successes. Dissent of all forms is merely a form of rhetoric, and it can help to create positive discussion and debate. Dissent in any discussion, while possibly not encouraged in the here and now, is necessary for giving an argument more emphasis and force.