In Parker v. North Carolina, the U.S. Supreme Court ruled in 1969 that a guilty plea is valid even if it was entered to avoid the possibility of a death penalty. The case involved Robert Lee Parker who pleaded guilty to first-degree murder charges in North Carolina state court at age 15, hoping to avoid capital punishment which was possible under state law for such crimes committed by individuals over this age threshold. He later sought habeas corpus relief on grounds his plea wasn't truly voluntary because he feared potential execution if he didn't plead guilty and went to trial instead. However, the Supreme Court disagreed with him unanimously (with Justice Thurgood Marshall not participating). It held that fear of a higher sentence doesn’t make a plea involuntary per se; rather, pleas are only invalid when induced by threats or improper promises causing involuntariness or ignorance about their consequences.

In the dissenting opinion for Parker v. North Carolina, Justice William O. Douglas argued that a guilty plea should not be accepted unless it is made voluntarily and with full understanding of the consequences. He contended that in this case, Parker's plea was influenced by his attorney’s incorrect advice about the death penalty law at that time in North Carolina - which stated that if he did not plead guilty but instead went to trial and lost, he would face capital punishment. This misinformation led him to believe pleading guilty was his only option to avoid execution; thus, according to Douglas' view, making it involuntary due to coercion or fear rather than an informed choice based on accurate legal counsel. Furthermore, Douglas emphasized how crucial proper legal representation is during such critical decisions as entering a plea – especially when life or death outcomes are possible – underscoring how vital it is for defendants’ rights under due process clause of Fourteenth Amendment.