S. Popov: The idea was that such weapons would be used at a very great distance from the Soviet Union. Using the very latest delivery systems, including missile delivery systems, somewhere in North America, and the resulting epidemic, caused by the use of ultra-virulent biological agents and with no chance that the public could be treated for those diseases, such a thing could take place only far, far away from the theater of operations.
The second explanation is that, paradoxical as it may be, the Soviet leadership could be... could deliberately contemplate the possibility of striking some number of their own armed forces, if the damage inflicted on the other side was much greater.