Document exempting MOOCs from Iran sanctions is here [1] in part (iii) It clearly exempts Iranian students from sanctions for undergraduate MOOCs and some more.
Coursera does the same. As an important contributor to education access, I expected more than indiscriminate banning of people, because of the country they are in while the law allows it specifically. Especially that is more important for Iranians under current the government.
It is important to be informed, the other option is to fall victim to the propaganda fed on national television to us every day.
For more context refer to list of sanctions and exemptions of Iran in treasury.gov [2] Iran License (No.G) contains more context.
[1] (https://home.treasury.gov/system/files/126/iran_glg.pdf) [2] (https://home.treasury.gov/policy-issues/financial-sanctions/sanctions-programs-and-country-information/iran-sanctions)