I'm cutting the 13 for my pocket with a firm stroke. I would want to give myself the best chance I can get to pocket the ball so whatever I need to do to accomplish that, that is how I will want to play the shot. I have also played the shot with a zig zag pattern on the cue ball, sending it side rail side rail towards the ball near my opponent's pocket. This I might do if I feel the three balls are ideally positioned. I've played this shot in this way numerous times with a high success rate. There is a reasonable chance I can leave the cue ball down low and along his side rail. If that happens he won't have much of a shot on it. Either way I'm shooting of my pocket in this situation.
As was stated by others, there are several ways to sell out the kick shot which is a purely defensive shot. The cut shot is not much more difficult, so for my money I'd rather go down swinging than I would ducking. This also sends a message. I know of no player who prefers seeing their opponent shooting at their hole verses playing safeties.
One more thing that favors the cut shot for me. If miss the shot but I over cut the 13, it will run three rails towards the top left corner essentially taking it out of play. I'm very likely still in the hunt should I sell out that one ball.
One other factor that was not mentioned. Is the 13 ball past the foul line? If it is than anyone contemplating the kick is asking for trouble.
Tom