Compared to any other weapon, this is simply not true.
How do you figure? Biological weapons have to be cultured, and its not like you can purchase the agent on the open market. Anthrax is not easy to grow: it requires tight environmental control to get significant yield (enough to make a weapon). Chemical weapons must be manufactured in a processing plant. Mustard gas and other blistering agents, although chemically simple, require a processing plant to yield enough to make a weapon.
A gasoline (call it napalm) bomb requires... well… gasoline.