When ROMs are available for download at no cost and hacks and translations are simply available in freely-available software patches, usually it is not for profit and therefore less of a morally challenging issue. But when you put this software into a cartridge and sell it, things start to weigh into the immoral area of the morality scale. Even in this illegal world, there degrees of ethics and moral compromises when selling reproduction cartridges.
Not every reproduction is illegal. For example, Beggar Prince was originally released in Taiwan in the 1990s, but Super Fighter Team secured the rights to it from C&E, translated it, fixed many (but not all) of the bugs and released it on a Genesis cartridge in 2006 and off and on ever since. You can buy Beggar Prince and other cartridges from Super Fighter Team secure in the knowledge that you are buying an authorized product. Similarly, Piko Interactive secures permission to release unreleased SNES games with the permission of the rights owners. However, the guy who runs Piko Interactive used to have a separate label called RetroQuest which sold reproductions without authorization.
Here are some categories of games where the moral issues of reproduction cartridges become increasingly difficult :
Games like Somari and Final Fantasy VII for the Famicom go in this category. In this case, the reproducer is a thief stealing from a thief. The Taiwanese and Chinese pirate outfits who programmed these games use graphics and sound and often code taken directly from the games whose success they are trying to cash in on. Final Fantasy VII for the Famicom also liberally helps itself to graphics from the Famicom Final Fantasies. However, there is usually some original content here. Does whatever original content lose all moral rights to protection because it is coupled with stolen content and sold with the intention of profiting off the creativity of others? If someone made a reproduction of Leisure Suit Larry and the Long Look for a Luscious Lover, it would also fall into this category.
Time Diver: Eon Man, the prototype versions of Maniac Mansion and Final Fantasy II, and Star Fox 2 fall into this category.
In this case, the original cartridges were usually supposed to be destroyed or returned to the publisher or developer. Other times, they were simply abandoned as trash when a company went out of business. In the first sense, the person who buys a prototype may really be buying stolen property. There is assumption that a 35mm print of a feature film in a private collection has a questionable chain of title. In the second, there are complicated questions of whether something was truly abandoned or whether the copyrights remain for the artistic elements or because of a finished game. However, video game companies usually had atrocious storage abilities, so the first scenario may very well become the second scenario if someone did not rescue it.
Especially in the case of prototypes which never saw an actual release, there is an important concern in preserving these games and distributing them far and wide. Star Fox 2 and Earthbound Beginnings are important examples of prototypes that should have been released then and provide a lot of enjoyment since. Unfortunately, copyright law will protect this software for as long as it would officially published software, so if it is not distributed, it could be lost.
In Earthbound Beginnings' case, Nintendo has recently made it available on the Wii U Virtual Console. This is unfortunately only one example of a prototype receiving official exploitation. There is no legitimate way to play Star Fox 2, which certainly was not intentionally abandoned, just not released.
3. Contest & Limited Time-Availability Games
I include Nintendo World Championships 1990 and its successors in this list. These games typically used unique hardware on their PCBs, making them unplayable as intended with ordinary hardware. Also, one should consider the Sega Genesis Sega Channel Games and the SNES BS Satellaview games as also falling into this category. The Nintendo Campus Challenges, 1991 (NES) and 1992 (SNES), and Nintendo PowerFest '94 cartridges also fall into this category. They were never released to the public but were playable by the public for a period of time, often short
4. Hacks & Translations
Hacked games like Zelda Outlands and Super Mario Bros. 3 Mix fall into this category. In this case, the reproducer is rarely reproducing his own work. In this case, the reproducer is profiting off the hard work of not only the original developer but the hacker, who released his hack to the public gratis.
Porting a Famicom game to the NES often involves applying a translation patch. Popular titles include Gimmick!, Splatterhouse: Wanpaku Graffiti, Final Fantasy II & III and Sweet Home. SNES games include large RPGs like Tales of Phantasia and Star Ocean. Not only do these games need to fit hardware, most have to be translated as well.
Japanese Famicom games are playable with a pin converter and a minor modification for those games with expansion audio. Japanese Super Famicom and N64 games are playable either by putting them in a SNES shell or breaking off a pair of tabs inside the SNES or N64. Sega systems require a pin converter (Master System) or a trivial mod (Genesis).
Virtually no reproduction outfit produces their own translations, they use the typical translations available at romhacking.net. (Super Fighter Team is a notable exception) Here is another ethical issue, not only is the reproducer profiting off the original game but the translator's efforts.
5. Extremely Rare Release
This is when you make a reproduction of rare games like Little Sampson or The Flinstones: Rescue of Dino and Hoppy. Collectors often react with scorn for these reproductions, even when the seller clearly states that it is a reproduction cartridge. Many rare games use common boards and can be converted with little more than an EPROM programmer and a soldering iron. Considering the high prices that sellers tend to charge for these, it is much cheaper to buy a NES PowerPak or Everdrive N8 and play these games with a multi-cart. Collector-oriented sites like NintendoAge and AtariAge have no compunction about allowing forum members to sell cartridges falling into ##1-4 but get into a real hypocritical frenzy when it comes to #5.
I am aware of video game completionists who have to have every game on their shelf. They may buy a reproduction to fill a hole, but while may satisfy their OCD-need to fill a hole, the reproduction will never legitimately acquire value anywhere near the real cartridge.
Consider Stadium Events, by far the most pricey of any licensed NES cartridge. It is estimated that only 1,000 survived the recall when Nintendo took over the distribution of the Power Pad from Bandai. Nintendo subsequently re-released it as World Class Track Meet, both individually and as a multi-cart with Super Mario Bros. and Duck Hunt. WCTM in both releases is very common and has only cosmetic differences with Stadium Events. There is no legitimate reason to make a reproduction of this game when the gameplay is so readily accessible.
Piko Interactive made a reproduction of Super Noah's Ark 3D for the SNES, but it obtained the permission of Wisdom Tree to release it. Its reproduction uses a standard SNES shell instead of the unique one the original release used. It also does not require an official cartridge to be plugged-in to a passthrough connector to bypass the lockout chip, unlike the original from the 1990s. Clones of the SNES lockout chip exist which will allow the game to work with regular consoles.