The argument is that America and Israel should have nuclear arsenals but Iran should not. Iran's critics run into trouble when they explain their argument since anything they might say about Iran goes double for Israel. Because of this, the explainations are normally left out. People are supposed to assume that America and Israel are the good guys deserving of nukes while Iran is not. This may have gone over better a decade or two ago before the truth about Israel was released upon the world, mainly through the internet. Israel has no credibility in the world, and America, in the role of Israel's stooge, has even less credibility.
Jerusalem light rail conductors striking over new train schedule (Haaretz)
from the article: Iran expected to reject proposal for nuclear fuel swap