Suppose that if we humans keep doing an activity, then we'll have at least a P percent chance of causing the most horrible series of events so far in human history within 50 years. How big does P need to be before it's irresponsible to say, "Well, the horrible event is unlikely to happen, so let's not worry about it"? 50% (1 in 2)?5% (1 in 20)?1% (1 in 100)?0.1% (1 in 1,000)?0.01%? (1 in 10,000)?0.001%? (1 in 100,000)?0.0001%? (1 in 1,000,000)? To me, it seems bizarre to dismiss a thre...