I don't see any reason as to why we should be politically against them. Out interests are currently one and the same. To liberate the Muslim world, decrease Israel's influence in the region, and create a more competent and dependent governments.
Didn't Iran help America and its allies against the Taliban? Isn't Iran helping Alawis against Sunnis? Aren't the minority Sunnis in Iran marginalized and disenfranchised? Weren't the Safavids partially responsible for the decline of the Ottoman empire? And what about what the four imams of the four madhabs warned us about Shias?
I'm not completely aware of Iran aiding America against the Taliban, but the Taliban like Al-Shabaab are a threat to everyone and anyone. They do not have a clear agenda, and their conducts of war are completely Un-Islamic and inhumane. As for Iran supporting the Syrian regime, that has nothing to do with sectarian division. But making sure that Iran does not lose another ally in the region. Other than Syria and Hezbollah, there isn't another single Arab country willing to fight along side Iran. The Saudi soldiers were sent into Bahrain to subdue Shia Bahrainis that were demanding their rights. Every minority group in the ME is disenfranchised and politically marginalized. When it comes to the fall of the Ottoman Empire. There are multiple factors that led to the decline of the ottoman Empire, the worst of them being the Great Arab Revolt. Sharif Hussein started it, and the Ottoman Empire fell because of the Arabs betraying the Caliph and siding with the British and French.
We can not fight internally, when we have external forces that are using us as a pawn against each other. There clearly exists a division and mistrust between the Sunnis and Shias, but when you look at the bigger picture today, the only MUSLIM NATION standing up against the West is Iran. We can not afford to see them destroyed.