Iran is on an unprecedented aggressive and violent push towards dominating the Middle East.
They are deployed in Syria, building forward bases to threaten Israel, destabilize Lebanon and pushing it closer to another war with Israel by funding and arming Hezbollah.
They are sponsoring and arming Shiite militias in Iraq and provide them with ballistic missiles to threaten other Middle East countries.
They are supporting and funding the Houthis in Yemen who are responsible for the civil war and attacks on Saudi Arabia and Gulf states. They are supporting, funding and arming Hamas and Islamic Jihad in Gaza, both of which are recognized terrorist groups intent on murdering Jews.
They are responsible for historical attacks on US forces in Lebanon during the 80s which killed hundreds of Americans. They are later responsible for the attack on the Jewish community in Argentina in the early 90s. Lately multiple Iranian operative cells have been exposed in Europe, trying to engage in assassinations.
They are bullying Gulf states. They are calling for the destruction of Israel every few weeks.
Iran is developing a ballistic missile program which is intended to threaten Western Europe (they are up to 4000km in range now with their latest missiles).
Finally, Iran hangs gays from cranes.
Now, why would anyone in their right mind oppose sanctioning this country?