A native speaker could say that, but only to mean something very specific: the only thing you should lock is file cabinets. Don't bother locking your front door or your bicycle or your car, but we've got file cabinet burglars in this town, and so those should be locked at all times. It would be a peculiar thing to say, to say the least, but not grammatically wrong if that's what you mean.Could you kindly tell me how strange/unnatural it would sound, if I said B1 “Well, yes, but you sholuld lock file cabinets."?
Is it something no native speaker would say, or sounds totally strange?