That link does not say that it's not dangerous. It is less dangerous than a bullet fired at close range, and it is not as likely to be lethal, but it still can be lethal, or cause serious bodily harm, and therefore it is still very dangerous.

Furthermore not all warning shots fired into the air are fired at high enough angles that the bullets decelerate to terminal velocity before hitting something.

Even if it reaches terminal velocity and doesn't hit anyone, in an urban area it can easily hit someone's property and cause property damage to roofs windows or walls.

True, but a bullet falling at terminal velocity may still kill:

http://articles.nydailynews.com/2011-12-20/news/30540094_1_a...

Edit: this particular bullet would have been on a ballistic trajectory and would have retained a significant amount of its original velocity.