The Safavid dynasty, which was founded in the 16th century, was known for its strong Shia identity and its efforts to spread Shia Islam throughout its territory, which included present day Iran, Iraq, Azerbaijan, and other areas. As part of this, the Safavids engaged in religious persecution of Sunni Muslims, including acts such as killing or exiling Sunni religious leaders and scholars, destroying Sunni mosques and graves, and using intimidation and violence to force conversions to Shia Islam.

As to why they thought it was okay to kill Sunni Muslims, it's likely that the Safavids saw their actions as part of their efforts to spread and solidify Shia Islam as the dominant religion in their territory. Additionally, there was likely a political opponent to their actions, as the Safavids saw the Sunni population as a potential threat to their rule.

As for why the Ottoman Empire, which was Sunni, did not assist the Sunni Muslims in Iran and elsewhere, it's likely that the Ottomans did not have the resources or the interest to intervene in the affairs of another Muslim dynasty. Additionally, the Ottomans and the Safavids were rivals and may not have wanted to aid a population that could potentially be used against them.

Regarding the silence of major Shia scholars such as Mohammad-Baqer Majlesi, it's possible that they may have seen the Safavid actions as necessary for the spread and protection of Shia Islam. Additionally, they may have felt that it was not their place to challenge the actions of the ruling dynasty. It's worth noting that historians and scholars have different perspectives on the actions of the Safavids and it's a complex subject with many nuances.