I'm not saying I don't understand it. People want a diverse game. But I'm with @Kaiju, personally. This issue is the source of weird feelings because it turns something that is a fact of life for many people into a character gimmick/bulletpoint/angle/accessory/niche/whatever other words were used for it above, and it's effing weird for people to be territorial about something like that. Being an amputee isn't a plot point in a story that belongs to one person, it's a thing that happens to people.
The big-picture concern (I assume) is, 'but what do I do if half of my game's PCs are suddenly amputees' and that sort of cascades into the conversation about whether or not 'uncommon' concepts should be restricted in PC populations (example: Force Users on a Star Wars game). Some people say yes. Some people say no. (I am in the 'no' camp, because I like fun, but ymmv.) I am sure MSB could do 50 pages of circular arguing on the point, though. I think an individual character's relationship to their own circumstances, physical and emotional and otherwise, is what makes them come to life. The variables just give them framework.
Gray Harbor does seem to exist on the edge of a hell mouth full of monsters or something, anyway. A couple of people missing limbs would definitely not surprise me. ¯_(ツ)_/¯