The "more reasonable" end of the argument is the idea that stressing the repressive character of the Iranian regime and our solidarity with its victims can only contribute to right-wing, pro-war propaganda and thus boost the drive to war. More reasonable than the SWP's hysterical denunciations, that is, but still totally wrong.
The idea that the US, British or Israeli ruling class will be more likely to go to war because socialists make solidarity with the left opposition in Iran is clearly ludicrous. But could our denunciations of the Iranian government "soften up" the working class and other sections of the population in, for instance, Britain for the ruling class' war drive?
Obviously we need to tie our solidarity with the Iranian workers etc to our anti-war stance - and do so clearly. But the underlying methodology, which thinks you can/should stop war by failing to highlight the character of the Iranian regime - or more generally oppose our ruling class by covering up the truth about the world - is wrong, and anti-Marxist.
It's an approach which comes from Stalinism. The Stalinists accused Trotsky, when he criticised and exposed the crimes of the Soviet bureaucracy in the USSR and internationally, as aiding the threat of Western military intervention in Russia. He replied scornfully - pointing out that the way to fight imperialism is for the widest possible layers of the working class and the people to be conscious, alert and in full possession of the facts.
The same is true today. An anti-war position which relies on lying about, or covering up for, the Iranian regime, and thus refusing to make solidarity with movements in Iran, is not just "morally" wrong, but weaker not stronger than an anti-war stance based on telling the truth. It fails to prepare the working class in Britain, the US etc for the tasks which face it, and bases opposition to war on the incredibly shaky foundation of whitewashing the Iranian regime. Much better the solid foundation of international working-class solidarity.