Foraging is finding ingredients in nature to use in cooking. Ingredient selection is a basic and perennial aspect of all cuisine, and to the extent that foraging (or horticulture, or hunting, or shopping) contributes directly to the cooking process, I think questions should be encouraged.
If people have access to wild ingredients and want to use them, or want to know if their area has any, that's a great thing to know. The question has to be asked well, of course. Queries which merely say, "can I eat this" are trite, arbitrary, and potentially dangerous.
Specifically, if someone took a picture of a store-bought olive, uploaded it, and wanted to know what variety it was, what region it came from, what its flavor notes were, and how best to pair it in a dish, there'd be no problem with it. What's so different about that and someone uploading a picture of a berry from the trail behind their house, or an herb they gathered in a field?
Phrasing and context will matter. "How do I incorporate local or seasonal food into menu-planning?" is a serious question that serious chefs ask all the time. "Which variety of basil grows best in an herb garden in the south" doesn't strike me as unreasonable either. I think it's better to have people ask it. Outside the line would involve plant breeding, genetics, classifications of species, specific techniques for gathering, hunting, or growing, or anything too regional to be useful for most readers. In short, "would a chef be able to make better food because they know the answer to this question?" seems like a good benchmark.
Mushrooms, truffles, some herbs, fruits, berries, even, theoretically, hunted game could be tangentially on topic. What about how to dress, store, or cook venison?
Foraging is not something only hippies, freegans and survivalists do; increasingly it's something that gourmands and foodies, traditional cooks and regional/nativist enthusiasts do. It is certainly something the ancestors of our great cuisines did. It is something we can do, too, with requisite knowledge, which is what this site can help to provide.
I understand the importance of keeping the site high quality, I just tend to disagree that fringe questions are the problem. I think more generally, bad questions are the problem. I don't have experience with SO, so I don't have history moderating; I'm just responding to my personal preferences: I'd like to know about these things, and think other cooks/chefs might too.