Yes, a UFO could be a deployment device for biological/chemical weapons (a supposition made by an earlier poster) but the severity of such a threat should be balanced by its probability which can be estimated with reasonable accuracy with appropriate intelligence....
I stated that it was POSSIBLE to distribute bio weapons this way - but I never supposed that this was the case. The problem for intelligence staff is that if you have an unidentified balloon there is no way of telling what it might be, short of examining it. And the easiest way to examine it is to bring it to the ground. If you can engage the object economically and safely, that seems to be the best course to take. What else would you have them do - find a way to examine it in mid-air?