The "slippery slope" argument is a logical fallacy used to publicly justify action which is desirable for other reasons (Realpolitik). Iran has other WMD (
chemical and
biological, as well as the easy access to radiological that any semi-developed country has) and has singularly failed to use them either openly or by proxy. Where do I think it will end? Iran will feel a bit safer and the West/Israel will have to treat them with a bit more respect than we do now.