I don't own a Metal Slug cart, what does the sticker say?
My guess is because in America, people will sue you for anything. Most other cultures are a little more sensible. On my Japanese DC, the warning sticker is literally only 1/3 the size of the american one. Most of the japanese versions sticker is english too. Liability pure and simple. WARNING: DO NOT PUT COMPUTER IN MOUTH. DO NOT POUR LIQUID ON IT. DO NOT STICK YOUR FINGER IN THE DISK DRIVE. DO NOT POUR HOT COFFEE ON YOUR PRIVATES.
All just the same thing: make sure you insert it properly otherwise you can damage your game/system, somewhat re-phrased. I wonder what knuckehead went & caused such a commotion that SNK would even begin printing those stickers in the first place.
Yeah, you guys are right, some idiot probably threatened legal action for their own folly, or took legal action against some other game company. If someone's kid starts twitching and swallowing his tongue because of something he plays, its his parents fault; they should be watching what he plays if they know the kid has that kind of problem. A sticker is good, but people here must be too damn stupid to read the waring labels so I guess SNK had to make them much LARGER so people would see them.