Leaving aside the racist origins of Saturday Night Special bans, Banning these guns makes it more difficult for honest, hard working people who with less money to spare to afford a firearm for self defense

An excerpt from the above article which illustrates the history of Saturday Night Specials:
“To prevent Blacks from arming themselves, southern states enacted the Black Codes, which “fixed the black population in serfdom, denying all political rights, excluding them from virtually any chance at economic or social advancement — and, of course, forbidding them to own arms.” (Don B. Kates, Jr., “Toward a History of Handgun Prohibition in the United States,” Restricting Handguns: The Liberal Skeptics Speak Out, Don B. Kates, Jr., Ed., North River Press, Inc, 1979.)

After ratification of the 14th Amendment (1868) and enactment of the Civil Rights Act (1875), several states responded by passing laws which on their face were race-neutral, but which in effect were not. Attorney Robert Dowlut observed, “It does not matter that a law on its face applies to all. A law will be deemed unconstitutional if the ‘the reality is that the law’s impact falls on the minority.’” (“Bearing Arms in State Bills of Rights, Judicial Interpretation, and Public Housing,” St. Thomas Law Review, Vol. 5, Fall 1992.)

Among these laws, the forerunners of so-called [junk gun] legislation, was Tennessee’s “Army and Navy” law (1879), which prohibited the sale of any “belt or pocket pistols, or revolvers, or any other kind of pistols, except army or navy pistol” models, among the most expensive, and largest, handguns of the day. (Such as the Colt Model 1960 Army, Model 1851 Navy, and Model 1861 Navy percussion cap revolvers, or Model 1873 Single-Action Army revolver.) The law thus prohibited small two-shot derringers and low-caliber rimfire revolvers, the handguns that most Blacks could afford.”

Wikipedia states the definition as:
“Legal definition[s] of a “junk gun” usually restrict the materials that can be used in the manufacture of said gun, targeting zinc castings, low melting points (usually 800 degrees Fahrenheit), powder metallurgy, and other low-cost manufacturing techniques. As nearly all guns made this way are in small calibers, such as .22 Long Rifle and .25 ACP, even these techniques provide sufficient strength for the low pressure cartridges and desirable weight and cost savings. The low strength materials and cheap construction do result in poor durability and marginal accuracy at longer ranges, but as most of these guns are very small pocket pistols designed for use as close-range backup defensive weapons, accuracy and durability over thousands of rounds are not primary design goals. Most guns targeted by the “junk gun” bans are made by a group of current or former manufacturers in the Los Angeles, California area, such as Bryco Arms, Jimenez Arms, Jennings Firearms, Raven Arms, and Phoenix Arms (the latter so-called because it “rose from the ashes” of Raven Arms, after the Raven Arms’ factory fire). Their guns sell for as little as US$50 new. Other legislation targets specific inexpensive models by highly reputable manufacturers such as Colt, Taurus, Smith & Wesson and Ruger.”

Banning these guns makes it more difficult for honest, hard working people who are poor to afford self defense guns.