I didn't read the quote as a blanket opposition to violence. It's a warning about one thing to consider before you choose violence.

I also didn't read the quote as only being about violence. It also makes a more general point about means and ends. When you're considering an action in pursuit of a goal, you should consider the action in its own right and try to predict where it is likely to lead. Don't settle on an action just because it seems to fit with the goal. This is especially relevant when you consider using violence, coercion, manipulation, or dishonesty for a noble purpose, but it also applies more generally.