Psychologically speaking: This is because it’s not your opinion. It’s hard to detect reason in things you don’t believe in.

That doesn't sound like climate alarmism to me at all. Proper climate alarmism would expect the economy to suffer. As you well say, if decarbonization was something that boosted the economy, it would happen on its own. In fact, an energy transition demands putting a very serious limit to economic growth, because at the very least during the time of the transition, that is supposed to last decades, you can no longer count on expanding fossil fuel extraction to power industry. Even supposing a smooth transition from fossil fuels to renewables and nuclear (a big if), renewables and nuclear both demand quite a bit more infrastructure investment than fossil fuels, so substituting the same amount of fossil fuel energy production to nuclear and/or renewables would be in effect detrimental for economic growth.

The important thing is, it still has to be done because there is no alternative. Fossil fuels are running out anyway.