You have to understand that nearly 40% of the Muslim world are unable to read or write, this is based on reports from the Organisation of Islamic Cooperation and the Islamic Educational, Scientific and Cultural Organization and it was reported in 2015.
People like that are easy to brainwash,convince and sway. And there is both a theological as well as cultural war against Iran these days. Propaganda, fake news and etc. People don't really understand what's going on unless they look into it themselves and the majority of people don't. Sectarianism, is something a lot of people bring up. But I've yet to see any influential or big people within Iran say anything Sectarian. However, there are many edicts and sayings from the other side where they say Shiites are this and that and need to be killed, solely because they are Shiite, or "Iranis". Keep in mind, that I'm not a Shiite myself. But I am Iranian.
I had an interesting conversation with a Turkish friend of mine, who's father is an Imam at a Mosque in one of the suburbs here, they are Hanafi. And they told me about the propaganda going on. And basically that Salafism/"Takfirism" is being spread like a wildfire in some of the Muslim communities, because there are certain countries promoting this around the world. And it's not a surprise that there are terrorist attacks and controversial things happening in the name of Islam.
These are the people that make the Muslim world look bad as well as causes strife and hate amongst the Muslims. These are the people that the west look at when they talk about Islamic terror and etc. But they don't know that there is just this group that is this way and instead generalise.
Anyway,
10-20 years ago, the hate against Iran wasn't like this. But thanks to theological propaganda and conventional propaganda, it is what it is. For example, Some people are so ignorant that they think there are no Sunni mosques in Iran and that the Sunnis are being executed for being Sunni and etc. And this is just some of the propaganda and bullshit being told about Iran.