In the 1906 case of Allen v. United States, the Supreme Court examined whether a defendant's constitutional rights were violated when he was not allowed to testify on his own behalf due to prior convictions. The court ruled that it is permissible for a judge to prevent a defendant from testifying if they have previously been convicted of perjury or other crimes involving dishonesty or false statement. However, this ruling does not apply universally; rather, it must be determined on a case-by-case basis depending upon the nature and number of previous offenses committed by the individual in question. In this particular instance, Mr. Allen had multiple past convictions which led to him being deemed an unreliable witness and thus prevented from testifying in his own defense.

In the dissenting opinion for Allen v. United States, Justice Harlan argued that the court majority had erred in its interpretation of reasonable doubt and burden of proof standards. He contended that it was inappropriate to instruct jurors they could find a defendant guilty if convinced "to a moral certainty" rather than beyond all reasonable doubt. He believed this language allowed room for subjective interpretations and personal biases among jurors, thereby undermining defendants' rights to fair trials. Furthermore, he disagreed with the majority's assertion that these instructions were harmless errors because they did not affect final verdicts; instead, he maintained such misinterpretations could significantly influence jury decisions and thus should be considered harmful errors warranting retrial or dismissal.