I’ve thought the same thing but I imagine the logistics would be a nightmare....bringing a bunch of volunteers who aren’t up to speed on weapons and don’t know the geography with no place to sleep. Plus you gotta’ feed them.
Bottom line is any and all who would volunteer would probably be best used as canon fodder.
Volunteers as in ex-military. Especially jet pilots.
Much like the AVG during WWII.
They already have top quality training.