Consider this: Someone hands you a SD card when you need to transfer some data between some devices. You think you delete it afterwards, but the SD card has hacked firmware that just pretends its been deleted. You hand the SD card back, and your "benefactor" now has your data.

It's a flaw if people are not aware of it. Most people see things like SD cards and USB sticks as "dumb" storage devices with no real ability to run software, and are totally unaware of the risks they can cause.

It can be a feature if people are aware of it.