why should america homeland security officals worry about biological weapon than chemical and nuclear weapons?

Answer 1

Much easier to bring in a biological weapon than the other two. You can give someone a virus and have him or her spread it around like say the Plaque, or Tuberculous, or a new strain and it could spread like wildfire, killing millions. You can put biologicals in soap, shampoo, shaving cream, and other household products and bring it through airports undetected. Much harder to do with the other two and you need major quantities to do any damage with chemicals.

Answer 2

They are THE weapons of MASS DESTRUCTION!
SECURE THE BORDERS!