Board Thread:Online Discussion/@comment-14350577-20131024162905/@comment-26801133-20150813205026

Here are 3 reasons:

1. Galmar Stone-Fist will execute him for you if the Reach is under Stormcloak control(you gotta leave some victims for others too, not just yourself.)

2. Use a frenzy potion on his soldiers and watch as they turn on him. More satisfying.

3. Dont use a dagger. Complete the quest and use the Ebony Blade instead.