1. Climate change is man made, but we still don;t have the tools to stop it (i.e. it's too late)
No, because we supposed here that it wasn't mostly man-made.
2. Climate change is not man made, but we can still stop it (i.e. it's too late)
How? Our assumption means the effects of carbon dioxide and other greenhouse gases is greatly weaker than we currently suppose. What's in our tool box at this point?
And I see repeated use of the phrase "it's too late". It's too late for what?
I didn't say that we were trying to make sure the climate was the same as 1850. The goal would be to negate any bad effects such as loss of biodiversity in ecosystems, disease prevention, famine prevention, etc.
Then why aren't you considering such effects with respect to proposed mitigation strategies? For example, a possible tool in the box is supposed to be reduction of carbon dioxide emissions via abandoning of a hydrocarbon based transportation system. But currently, that means abandoning a huge amount of infrastructure and knowledge with a rather large negative impact on society.
Sure, down the road, it might not, say because hydrocarbons from fossil fuels and other sources grew expensive enough to obsolete this infrastructure. But that's a huge economic change with large negative consequences for which embracing an early transition seems poorly advised. Especially since it can result in the same "loss of biodiversity in ecosystems, disease prevention, famine prevention" though perhaps with greater effect.
Also, it's worth noting that none of the above problems is particularly reliant on climate change and there are fixes that whether in the presence or absence of climate change that could greatly reduce the problem. Loss of biodiversity is primarily a result of habitat destruction that hasn't almost nothing to do with climate change. It can be partly fixed by dedicating land, particularly corridors to allow movement of species to new biomes (as would be necessary under a significant global warming scenario). Disease and famine prevention is primarily a result of fixing dysfunctional societies - it's not a feature of developed world societies.
I am not saying those things will definitely happen, but it is certainly worth trying to stop if there is a reasonable expectation that they will happen if we continue on our present course.
Only, if they're more likely to occur than if we choose other paths. That's part of the point of a cost-benefit analysis. You look at the costs and benefits of every choice relative to other choices, not strictly the benefits of the choice you'd like to make versus the costs of the choice you don't want to make.
One of the problems I see here is that climate change is greatly weighted as a concern relative to other, bigger problems of humanity such as poverty, corruption, disease, desertification, overpopulation, etc. There's little consideration of how the proposed solutions for global warming will effect these bigger problems or conversely how not addressing these bigger problems as effectively (due to our skewed priorities) will effect our ability to address global warming.
The current "do nothing" strategy actually has profound effects on the bigger problems. It increases human wealth and higher value of female labor both which are negatively correlated with all of these problems. Conversely, the wealth destruction of a possible AGW strategy could result in increases in these big problems which in turn tend to work against both the global coherence of an AGW strategy (by increasing the relative effect of these problems with respect to AGW issues) and the societies themselves, meaning there is a negative feedback working against the proposed strategy which isn't being considered.
Even if that wealth is going to be destroyed anyway due to a "peak oil" situation, being destroyed in a distant future is less costly than being similarly destroyed today due to economic time value.