Well, the ability to kill anybody at a distance, with likely no consequences would be...well, I don't want to say 'too much power for one person', but it's too tempting to overused. It's like having a cheat code in a video game. You use it once to get past a really difficult part and try never to use it again. But then you do. Eventually, you're using the cheat code every ten seconds.
Then again, maybe not so much. Especially if it makes the news. While I usually don't like to rely on the goodwill of humanity, there is a certain amount of inherent goodness in most of us.
If I had such a weapon, I'd try my damnedest to limit how often it's used, but there are a few major figures who's death I believe would greatly improve the world. But, even then, I'd really have to pray about it before actually using it.