...The Federal Firearms Act is prospective only. That is, under it no one in the class described may be convicted for having transported or received either a firearm or ammunition at any time prior to its passage. In the ordinary sense, then, it is not an ex post facto law. But the appellant contends that it is an ex post facto law as applied to him because it imposes upon him an additional penalty for a crime which he committed and for which he was convicted before the Act was passed. The cases upon which he relies are [Cummings v. Missouri, 4 Wall. 277, 18 L.Ed. 356; Ex Parte Garland, 4 Wall. 333, 377, 18 L.Ed. 366, and Pierce v. Carskadon, 16 Wall. 234, 21 L.Ed. 276.
The Supreme Court in Cummings v. Missouri and in Pierce v. Carskadon struck down as ex post facto laws and therefore unconstitutional under Article I § 10, provisions of a state constitution and of a state statute, respectively, requiring the taking of a test oath containing affirmations of past loyalty to the United States in acts and deeds, and even loyalty in words, desires and sympathies, in the first case as a pre-requisite to pursuing certain professions and avocations, and in the second case as a prerequisite to filing a motion for a rehearing in a judicial proceeding of a specified type. In Ex Parte Garland the Supreme Court struck down as an ex post facto law, and therefore unconstitutional under Article I § 9, an act of Congress requiring the taking of a similar but less far reaching oath as a prerequisite to admission to practice before the Supreme Court of the United States. At first glance these cases may seem to support the contention of the appellant, but an examination of the opinions shows that they do not. In these cases the Supreme Court held the legislation invalid because it concluded that the test prescribed was not a test of fitness to practice the professions or avocations in question or to file a motion in court, and so that the legislation, in effect, imposed either an added punishment for a past crime or a punishment for a past act which was not punishable under the law as it stood when the act was done. In the dissenting opinions in these cases it is cogently argued that the statutes under consideration were not ex post facto laws at all, but we need not enter that controversy because even under the rule established by the court in those cases, as it was later developed, we do not think that the Federal Firearms Act is ex post facto.
In Dent v. West Virginia, 129 U.S. 114, 128, 9 S.Ct. 231, 235, 32 L.Ed. 623, cited and quoted with approval in Hawker v. New York, 170 U.S. 189, 198, 18 S.Ct. 573, 42 L.Ed. 1002, the Supreme Court, after noting that the doctrine of Cummings v. Missouri had been affirmed in Pierce v. Carskadon, said with reference to the Cummings and Garland cases "They only determine that one who is in the enjoyment of a right to preach and teach the Christian religion as a priest of a regular church, and one who has been admitted to practice the profession of the law, cannot be deprived of the right to continue in the exercise of their respective professions by the exaction from them of an oath as to their past conduct, respecting matters which have no connection with such professions". The court then went on to say: "The constitution of Missouri and the act of congress in question in those cases were designed to deprive parties of their right to continue in their professions for past acts, or past expressions of desires and sympathies, many of which had no bearing upon their fitness to continue in their professions."
In Hawker v. New York, supra, a case in which the Supreme Court upheld as valid a statute of New York which prevented one who had been convicted of a felony from thereafter practicing medicine, even though the conviction ante-dated the passage of the statute, the test is indicated by which the validity of a statute of the sort under consideration may be determined. In this case the court clearly indicates that the test is not the form in which the legislation is cast, but its substance, and that if, regardless of form, the statute in substance inflicts an additional punishment for a past offense, it is bad as an ex post facto law. But, on the other hand, this case establishes that if the statute is a bona fide regulation of conduct which the legislature has power to regulate, it is not bad as an ex post facto law even though the right to engage in the conduct is made to depend upon past behaviour, even behaviour before the passage of the regulatory act. This case also establishes that conviction of a crime may be made the conclusive test of past behaviour.
Thus if the past conduct which is made the test of the right to engage in some activity in the future is not the kind of conduct which indicates unfitness to participate in the activity, it will be assumed, as it must be, that the purpose of the statute is to impose an additional penalty for the past conduct. If, however, the past conduct can reasonably be said to indicate unfitness to engage in the future activity the assumption will be otherwise. So, in conformity with this principle, the cases cited above establish that a state cannot make past loyalty to the United States extending to words, desires and sympathies a test of fitness to teach, preach, practice law, or file a motion in court, and Congress cannot make such loyalty the test of fitness to practice before the Supreme Court of the United States. The constitutional provisions which prevent the passage of ex post facto laws by either a state or the federal government bar the way. But, on the other hand, a state can make conviction for a felony a test of fitness to practice medicine.
By the test indicated the Federal Firearms Act is clearly not an ex post facto law invalid under Article I, § 9, of the Constitution. Looking at the Act as a whole it is abundantly plain that in enacting it Congress was in no way interested in imposing an additional penalty upon those who at some time in the past had been convicted of a crime of violence. In the Act Congress sought to protect the public by preventing the transportation and possession of firearms and ammunition by those who, by their past conduct, had demonstrated their unfitness to be entrusted with such dangerous instrumentalities, and certainly no one can seriously contend that the test of unfitness which Congress established is irrelevant to this purpose. Surely it is reasonable to conclude that one who has been convicted of a crime of violence is the kind of a person who cannot safely be trusted to possess and transport arms and ammunition, and the fact that he may have reformed or that in some cases the test may operate harshly, does not invalidate the test. Hawker v. New York, 170 U.S. 189, 197, 18 S. Ct. 573, 42 L.Ed. 1002. See, also, McDonald v. Massachusetts, 180 U.S. 311, 21 S. Ct. 389, 45 L.Ed. 542....