i don't think there is any reason to leave them out entirely, though cabbage can be a problem with oxalates (and the whole brassica family)
again, probably a kidney thing, since oxalic acid forms a highly insoluble solid with calcium
Discussion
Spinach and rhubarb are oxalate heavy. So is tea. Anything that makes your teeth feel dry is probably oxalate heavy.
But cabbage and brassicas aren't.