These are fair questions.
> Why?
Because releasing energy is invariably accompanied by change of some sort. If that energy is released as part of an intentional effort by a technological civilization, then that change is also going to be intentional. The entities releasing the energy are doing it in order to produce change. That's the whole point.
Note that the situation we are facing here on earth is actually not what you would expect from that dynamic. Our current climate change is not directly related to the changes we've unleashed with the industrial revolution. It's an ancillary side-effect, and a particularly annoying one. But even if we didn't have CO2 to worry about, sooner or later we would cause some other change that would disrupt the previously prevailing equilibrium. In fact, we've already done that in numerous smaller ways. Lots of species and non-technological civilizations have already gone extinct here on earth.
The fundamental problem is that industrial revolutions produce exponential growth, which is not sustainable. Sooner or later that growth has to stop. (Even an arbitrarily advanced civilization is constrained by the speed of light to grow at a maximum rate of N^2 in the long run.) So either we have to decide to stop it or the laws of physics will do it for us, and the former seems unlikely.
> why a change in equilibrium universally results in catastrophe?
It doesn't necessarily, though it is very likely to be a catastrophe for someone. In any major upheaval there will be winners and losers.
The reason I think it's likely is that there will always be a period where new technologies cause living standards to improve dramatically, and that induces techno-optimism, a belief that technology will always be able to solve any problem that happens to come down the pike. Techno-optimism will cause civilizations to go closer and closer to the edge of the existential precipice because the Malthusians warning about existential threats will always be empirically wrong until it's too late.
> We actually found alternatives to fossil fuel long before we reached a crisis point.
Yes, that's true. And it's quite possible that on a different trajectory it would have taken 1000 years or 10,000 years to reach the crisis point instead of just a few hundred. But what is killing us now is not CO2 per se, but rather techno-optimism and the prisoner's dilemma. No one wants to sacrifice their standard of living for the greater good of future generations. And that seems to me to be a universal dynamic.