I always have done my infills without an electric file or drill. On P/W there are many times when I think it might be easier with it, to be honest, but as I have no training and don't do heaps of P/W infills, I've not pursued training. It does take FOREVER to manually file (compared to a drill), and a certain "finesse" (for lack of a better term).
The drill doesn't cause the damage its the improper use of them (just like guns, drugs and anything else that could be harmful if abused). If you want to use one, get the training, and practice practice practice before using on a client (like everything else)
Good Luck