Holmes isn't planning on conquering Asia, is he?
Who knows what's going on in that brain of his!
Well yeah, as despicable as it was, Magnussen was only using his powers to control people and make them suffer, not actually kill them. Which is why I think a more elegant and inspired solution was required from Sherlock, and why shooting him seemed so incredibly over the top.
Given there was a report that either the politician or her husband had comitted suicide it seems likely that, even if indirectly, Magnusson was killing people.
If memory serves, the politician on the hearing board was arrested on corruption charges or something very similar and the husband commited suicide.
CAM didn't kill people himself, but with his media empire and his knowledge, he would publish stories that would mean people ended up dead one way or another.
Shooting him in the head, destroying the brain was the only way Sherlock could have resolved the situation.