Personally, I believe the concern and outrage is warranted even if the death toll is indeed only (!) the 3,000 claimed by Iranian state media. That is the most conservative number so far and it is still an almost unimaginable number in such a short period of time.
It's not unimaginable at all. There are over 1200 cities in Iran, 400+ which saw active protests. If say, 'just' 50 were killed in each on average, that very quickly adds up to the tens of thousands. And looking at the footage coming out and the widespread news of overflowing morgues throughout the country, it's not unbelievable at all.
When people imagine mass casualty events, they imagine something like Verdun or Hiroshima, where tens of thousands are killed within a relatively concentrated geographic radius. But more often than not, they actually occur across a wider area in numerous but smaller casualty increments which add up to something much bigger. And when considering how deadly even a single well-positioned gunman with an automatic rifle can be against a crowd of unarmed and tightly packed civilians, it's really not surprising to see how easily casualties could have mounted, especially when you multiple that over 400+ cities.
Unfortunately, the major European players have generally proven to be utterly lacking in geopolitical foresight and incapable of acknowledging (much less taking credible action against) imminent or active threats until they smash down the front door, and as they did with Russia, China is no exception.
If Europe is to become the independent power bloc it loudly proclaims it will, it needs to understand that they need to expand their horizons beyond their immediate periphery. It cannot simply continue to pretend that the the affairs of the world outside of the EU borders are immaterial like they did in 2014.