What you've said is true. There are frequent disasters in societies of USA. Sometimes they are natural, sometimes social, and sometimes political. After 9/11 the safety questions for international students have risen up distinctly. Even after some disasters, USA cannot be considered as a risk zone. It has over 10,000,000 international students pursuing education. For them all, US government has been able to provide great security. Sometimes, despite of this security, some accident occurs but I think this occurs in other parts of world too. Staying anywhere isn’t hundred percent safe. You might not be safe at your own home then how can you be completely safe far away from your home? I don’t see any problem to remove USA from you abroad studying country list for safety reason.