If you mine a block but then delay the news so you can secretly work on another one, you risk getting orphaned as someone else sneaks in ahead of you. Working on unconfirmed blocks is pure gambling that kills your hash-power.
If you secretly buy out all the miners, being a benevolent controller who never reveals himself is likely to be more financially rewarding than attempting some destructive publicity stunt like a double-spend attack. In an unusual move, there seems to be a tendency towards less corruption as political power grows.
Even if someone with non-financial motives wanted to destroy Bitcoin, they could probably do it, but the cat's so far outside of the bag that it's on the other side of the river.
..But who cares. As they say: buy the rumour, sell the news.
I read the paper cursorily and it looks like an academic exercise because it's difficult to model luck and variation. 
