My interpretation of the line 'our mistake'; is more about taking responsibility on any and perhaps all levels and understanding the relevance (or irrelevance) of your actions no matter how involved or un-involved you think you are, and recognising what went wrong, appreciating the origin of the 'mistake'. Everyone always points fingers; we love scapegoats to explain away everything bad that happens to anyone. I think 'our mistake' is an attempt to step back from all the blame and just let your own choices reflect what you want the world to be like, even if what you see around you isn't reflecting those choices. Being true to yourself is the best course of action to stop these kind of travesties from continuing. And especially when it's not literally "your" individual mistake, you can still appreciate taking responsibility for your own actions (or lack of action) and for the reflections of various aspects of yourself that are occurring in society. At least.. we should be taking responsibility for ourselves like this..
We can separate it from ourselves and pretend like it's nothing to do with us, but that's just playing the blame game again. Instead or taking responsibility. You might think YOU don't need to take responsibility, but is someone else gonna willingly take that blame first? No. But if EVERYone took responsibility for themselves and understood why they make the choices that they do, and how that effects themselves and the world around them. Then we wouldn't find the need to blame anyone for anything.
Might be a bit of a loaded interpretation. But my gut tells me that a line about generalising humanity as making a collective mistake, would have to come from a similar perspective. So that's how I comfortably interpret that line through my own belief systems.