Simply so, are electric knife sharpeners bad for knives?
Most single stage electric knife sharpeners (especially “free” sharpeners built into the back of electric can openers) damage knives. They use harsh abrasives which throw sparks (indicating the edge is overheated), remove too much metal and can gouge knives.
Correspondingly, can I use a belt sander to sharpen knives? A belt sander is a robust tool that is most useful for woodworkers. While rarely used for metal works, it does not mean that it is not useful for any other task. With the same power and efficiency, a belt sander is used for making as well as sharpening knives.