Symptoms of acute (short-term) exposure to high levels of hydrazine may include irritation of the eyes, nose, and throat, dizziness, headache, nausea, pulmonary edema, seizures, coma in humans. Acute exposure can also damage the liver, kidneys, and central nervous system. The liquid is corrosive and may produce dermatitis from skin contact in humans and animals. Effects to the lungs, liver, spleen, and thyroid have been reported in animals chronically exposed to hydrazine via inhalation. Increased incidences of lung, nasal cavity, and liver tumors have been observed in rodents exposed to hydrazine.
This does not sound like your family safe chemical that one would want in a heavily populated area like say, a massive Chinese city. The short-term exposure levels are enough to put a human being in a coma. Sounds pretty serious to me. And last time I checked, China does not have the health care capabilities to deal with chemical exposure of this magnitude.
The satellite was the size of a bus. Imagine the damage this would cause if it were to strike a building. There would be little chance of survival, and those who did survive would be exposed to the massive amounts of hydrazine. The US was unsure of what form the hydrazine would be in when it reentered Earth's atmosphere as well. If it was in a gaseous state, the damage could be much more extreme. Either way, it is possible for thousands of people to die if a satellite the size of a bus, carrying a toxic material, were to crash into a large building filled with people. The fact that hydrazine is a carcinogen does not help either. Those who are exposed to it have the potential to develop tumors also.
I admit that the chance it would hit China and even a population center in China is very low, but it is still possible. I would hope that you would not be "laughing aloud" if the satellite were to hit Beijing or Shanghai. Just the same, many people thought it was highly unlikely that 2 planes would be flown into the same building within minutes and another into the Pentagon, and I know there were not many people "laughing aloud." It was also a great shock when the levies broke in New Orleans and a city was devastated after Hurricane Katrina, and I would venture to say that not many people were "laughing aloud." I do believe that the US did shoot this down mainly to show that they had the capability to, and I also know that they did not want any country to have their hands on the technology that was displayed in this satellite, but the US also does not want to tarnish an already questionable international image by being responsible for a satellite landing in a Chinese city and killing and injuring thousands of civilians.
I recognize that the debris caused by the destruction of the satellite is not an issue. I thought that I had made that clear in my previous post with the joke that China was worried only because it may obstruct certain views of their current satellites. I would expect that the death toll from hydrazine exposure would increase to a much higher number than 1 if the satellite were to hit a population center. So next time some unbelievable tragedy rocks the international scene, I hope that at some point in your life, you did no "laugh aloud" at the previous thought of such an event taking place.