Why are the French (and Italians who are already at the numbers feared) not having children?
The why is a very difficult question, some of the underlying causes here are in the realm of wicked problems, but concerning Macron proposal population aging in France is a fact. Which is affected by ever
increasing life expectancy and decrease in fertility. For perspective in 1950, four workers were financing one pensioner, today this halved and by 2040 this is expected to fall to 1.3 workers per one pensioner.
Overall France has the lowest retirement age in OCED, with 14% of its public spending goes toward its pension (the highest of any except Greece and Italy), economy wise they are in the EU's "global south", with multiple economic challenges ahead including but not limited to the unexpected Putin's war, which put an end to Europe's peace dividend for starters. Overall, I think the decision to raise retirement age has merit.
The difference between this and the nitrogen emission is that emissions makes life worse for everybody for the foreseeable future.
I am not sure I agree with this framing. You can similarly side step the issue in France saying that impending deficit will make life worse for everybody, and focus on tradeoffs regarding Netherlands government decision to halve the country's livestock in few years which its proponents argue will threaten the economic, social and cultural viability of rural Netherlands.
Regardless the similarity I was referring to meta wise, concerning how the populist seem to be exploiting these incidents for broader antigovernmental protest bashing on these piņatas for all their electoral worth for the long run.
The problem is Macron side-stepping the democratic process.
I am not sure it is undemocratic. From what I skimmed it seem like part of the democratic game (to date it have seen the most use by a Socialist PM who passed minimum social assistance welfare program) and has a built in no-confidence vote, and failing that the decision could be overturned next time.