The interesting thing is that I remember The 10 Commandments winning a lawsuit against VHS in damages because those who can watch The 10 Commandments at any time instead of (I think) once a year would not bother to watch the commericals that coincide with the official screening, thus losing profits.
I remember the exact opposite.
If there was a way to legally digitalize the content along the lines of Sony's UMD Passport (which unfortunately only worked in Japan and for a limited time) then this crusade would be entirely justified, but this is not the case. As it stands today, flashcarts have a primary non-infringing use and the fact that they are mostly used for piracy is irrelevant because piracy is a crime committed by an individual, not by some evil criminal mastermind somewhere in China who plots to destroy Nintendo or game developers, they merely supply the market with a product that's in high demand and what the end user does with it is really none of their concern, much like a disc writer manufacturer isn't concerned with the fact that their hardware might be used for burning illegitimate copies of media.
Going along Nintendo's line of logic, we should ban TiVo boxes because they record footage, even if only for the sake of fast forwarding or rewinding. While we're at it, let's ban cameras altogether because those too can be used for camrips, no matter what anti-piracy protection is used. Hell, we should heavily restrict the Internet - the primary source of all pirated content in the world.
If you want to take the fight somewhere, take it to the individual committing the crime, not the manufacturer of the hardware used. When someone gets stabbed, nobody's going to sue the company which made the knife used in the murder because that's stupid. When a car accident occurs due to the driver's negligence, nobody's going to sue the car manufacturer because it's the driver who's at fault.
Banning hardware does not solve the problem - it merely strips legitimate users of their statutory right for making and using a backup. Nintendo is not harming illegitimate users because illegitimate users don't buy software for the most part. You're not "losing a sale" when said sale would not occur in the first place, no matter how you slice the cake.