The fact that climate change is a problem doesn't imply that there's a "right" climate. The rapid rate of change itself is the problem - and particularly the fact that that rate of change is faster than organisms and systems can adequately adapt to.

Atmospheric CO2 levels have previously, naturally, been higher than they are today. The most recent time that they were that high, the land on which most of our population's biggest cities were built was underwater. We could have just as easily built cities in an environment in which CO2 levels and temperatures were higher than they were in 1800, just by building farther back from today's coasts - but we didn't, so some cities will face massive costs to adapt, and others will simply go away.

All of that is literally true for cities, but it's also true by analogy for organisms and natural ecosystems. We can't quantify the full magnitude of climate change's impacts on those ecosystems, but there's wisdom in risk aversion when dealing with highly uncertain situations.