If you have a 1% probability of reversing the last 6 blocks, then you have about 28.5% of the total hash power. That can only happen if there's cooperation between 2 or more of the mining pools. So, yeah, it's a big gamble since that is likely to ruin huge businesses.

But, what kind of transaction moves so much money and can be successfully double-spent that way, at the same time? I mean, if the USA agreed on paying 10,000 BTC to Putin for, say, buying a lot portion of Russia's gas, and somehow managed to double-spend that, first of all, they wouldn't get any gas since it'd take some days (hundreds of blocks) to deliver, and second, that would probably be the reason to officially set sail to the second cold war.