And I'd say that what's good for the planet is not what's of concern. What's of concern is what's good for humans on the planet. Earth has gone through various states when it comes to lots of different aspects, when it comes to various environmental conditions. It does that naturally and would of course do that whether humans were here or not. The issue is, are certain conditions better for human life. And generally speaking the conditions that we evolved in are those that are best for us, except to the extent that we have enough time to evolve to be well suited for changing conditions. There are also issues related to how we've chosen to organize societies. Agreed and I meant that. I, poorly, chose to play along with the silly narrative that 'what's good for mother earth is good for us'
So it isn't just that conditions change. The issue is how fast they change and whether we as a species (and as societies) can evolve quickly enough such that the changing planet remains hospitable for us. The (perhaps somewhat cartoonish) story of the dinosaurs isn't that they dominated life on earth for a long time and then conditions on earth changed so they all disappeared. It is more so that they dominated life on earth for a long time (even, surely, through some changes) and then at some point conditions changed so quickly that they didn't have time to evolve to be able to prosper (or even survive) in them. To the extent any of them survived it was because they were the ones that were able to evolve quickly enough.
If a particular change would normally happen over the course of a hundred thousand years, but some event (or, e.g., some human activity) causes it to happen over the course of five hundred years, that matters. Those aren't, from the perspective of various forms of life on earth, the same things. From the earth's perspective, she will be fine. Even if certain conditions are for some reason better or worse for her, she has processes whereby she can regulate them within ranges. For instance, if carbon levels in the atmosphere get higher than she wants (assuming it matters to her), then she has ways of converting atmospheric carbon to subterranean carbon. And she has ways of converting active energy into stored energy. To the extent we reverse those processes and she isn't happy with that (again, assuming that for some reason she wouldn't be - which I don't necessarily do), she has ways of putting things back as she would want them to be. The issue is, does it harm human life as it currently exists - as it has evolved to exist based on different (and typically more slowly changing) conditions?
The planet has survived (and will continue to) through far more extreme conditions (assuming whatever baselines we might) than we could cause - even assuming we do have much such impact. But what conditions - as differing from those we've evolved to this point under - will humans be able to adapt to and thrive in? As we currently exist, we would surely not prosper under some of the conditions that have existed on this planet in the past.
Your point about the linear accumulation of carbon in the atmosphere is an important one though. I wouldn't phrase it the way you did, but we're thinking about the same basic question. It's one we don't really know the answer to yet, and it may be the most important one left.