Well they can control devices and machines, just not that way. They can use redstone signals, network signals and they can also be upgraded with a transposer which allows them to use items and fluids. IMO the transposer is the most useful out of those.
I agree, it would be good if certain peripherals could be whitelisted, and they'd have to be next to the microcontroller, not connected with cables. They don't want you to be able to connect screens and keyboards, but some things are more like redstone than like screens and keyboards.
