Which countries are allowed to own ABC-weapons?

The "ABC" items (usually called "NBC" in the US) are covered under 3 different treaties.

Nuclear weapons fall under the "Treaty on the Non-Proliferation of Nuclear Weapons" and the "Comprehensive Nuclear-Test-Ban Treaty".

Chemical Weapons come under the "Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on Their Destruction"

and Biological weapons fall under the "Convention on the Prohibition of the Development, Production and Stockpiling of Bacteriological (Biological) and Toxin Weapons and on their Destruction"

All of those treaties can be found on the UN's WWW site at: http://disarmament.un.org/wmd/index.html

With all 3 treaties the countries that had them when the treaties were signed ageed to work towards reducing the numbers maintained and to not pass the weapons or technology to other countries. The other countries (like Iran, Iraq, North Korea, etc..) that you refer to that signed those treaties also agreed not to develop those weapons.

It isn't a "blame them for having them.." it's blaming them for violating an International Treaty they agreed to uphold.