Modern civilisation wasn't around some tens-hundreds thousands/millions of years ago. It simply doesn't matter, it's not relevant, it won't change the argument: we are heating the Earth faster than in any other time period we are aware of, it's real, it's happening right now, and it doesn't matter that the Earth might cool or warm naturally over a span of dozens/hundreds thousands of years or more, we haven't been through it, we don't know, empirically, what will happen to us and other species, and we aren't prepared for it either.

And I never understand this argument, so what it's happened before? Our collective knowledge and intelligence has a pretty good consensus that we will experience consequences ranging from harsh to apocalyptic, no scenario predicts a good outcome, why be pedantic about "akshually, the Earth has been warmer before"? It does not add anything important to the discussion, it's just trivia.

Edit: on the topic of trivia, xkcd has a nice relevant chart [0]

[0] https://xkcd.com/1732/

And your point is? Humans evolved in that last tenth of the chart, and established modern society in the last pixel. I'd rather not our extremely fragile global society get disrupted by temperature fluctuations.