This is a country that took in Nazis by the bundle, what do people expect? Argentina is fundamentally a "white power" country and it shows. In another point, I remember telling people that BRICS expansion has to be strategic, by including a country like Iran you'll raise suspicions about it and will lend credence to western claims that it's an anti-democratic club. Iran is not necessary when you already have Saudi Arabia. Didn't see the point of Ethiopia either when you have Nigeria, the largest country in Africa and it's largest economy.
Including Iran is actually a very positive move because it shows that if a country makes an effort to move closer to China (and Russia) there is something to be gained. That should encourage others to follow in the same path. Adding the UAE and Saudi Arabia at the same time really symbolises that China's peace brokering in West Asia is sustainable and builds the foundation of a new regional dynamic built on peace and prosperity rather than sectarian violence
It's also very important to not give the US a veto on who is allowed to join the BRICS. By admitting Iran, the BRICS countries are telling the whole world that it's not up to America to decide who's isolated and who isn't. If you're going to take western concerns into account when deciding on new members, then what's the point of BRICS?
Not sure why you mentioned democracy, compared to Egypt, Saudi and UAE, Iran is the most democratic, but that hasn't really helped them, has it