The major problem of nuking something like that is that you can get more pieces that are out of the control. The goal is just to deflect. It's harder than it appears.
I'm aware of that problem. However it turns out that if the pieces you get are small enough, then they will individually burn up in the atmosphere without causing damage.
Moving most of a 50m rock out of the way and creating a bunch of small debris in the process is probably OK because the debris pieces are unlikely to be big enough to get through the atmosphere. (Satellites in orbit would be put at increased risk.)
Attempting the same on a 500m rock would be a different story.
Not only that - if you blast the thing into small pieces, most of them may miss the Earth completely. You will still have to track a lot more objects, but between being dead and having to fund such a project, I am certainly in favor of #2
They are completely different things. Star wars was meant to intercept immediate threats minutes after detection with light sub-orbital missiles with conventional warheads. A deep space shield would be Energia or Delta IV-class boosters with high-yield nuclear payloads meant to intercept targets years away months after detection on varied mission profiles adapted to the composition of the specific threat. It's a completely different game.
