`except` is a bad idea because it's a black-list, but what's wrong with using `slice` as a white-list? (Anyway, I just grepped our code and there is only ONE u

`except` is a bad idea because it's a black-list, but what's wrong with using `slice` as a white-list? (Anyway, I just grepped our code and there is only ONE usage of slice in a controller anyway, the rest are explicit, non-mass assignments)