Elsewhere in this thread people are literally talking about nationalized healthcare systems where people are waiting hours for ambulances, or dying in hospital waiting rooms. I think the statement of "normal people don't want to ruin the environment around them" is applicable to the people working in those healthcare systems, yet it's still apparently happening.
Private companies pollute because dealing with externalities costs money. It's not a problem they're trying to solve, it's a feature they implemented to increase margins.
The NHS doesn't have appropriate funding. If you increase funding you fix the problem. From what I've seen, the NHS used to be great until the 90s when the cuts began.
Remember Noam Chomsky's quote on this subject? "Privatisation technique: defund, make sure things don’t work, people get angry, you hand it over to private capital". The latter part is already happening.
No, the problem does not go away. You start optimising for short term political goals (see also: ongoing property debt crisis in China), and minimising short-term drama (see also: regulatory capture by unions). Sometimes you also start implementing insane projects just because your glorious leader decided to do them and cost/value is not an issue (see also: Chinese war on sparrows). Sometimes you just minimise the expense and make everyone disagreeing with you shut up, because they don't have a choice either way (see also: Chernobyl not having containment). You also get way less feedback, because you're spending someone else's money (i.e., taxpayers'). So no, "government consists of decent people and they won't optimise for the short term even though they are doing it now because there'll be no commercial company controlling it" is a very optimistic take at most and definitely not a realistic one.
Neither government agencies or crown corps are perfect, but at least they're not inherently flawed either. Yes they're subject to different circumstances than market companies, but that can be dealt with. Capitalism's inherent drive to cut corners and destroy the environment can't.
Other places in Europe seem to be even worse. For example, I've seen people from Ireland shocked that thsi would happen and preaching the benefits of their state-owned water and their fight against privatisation and water billing. There are places there which literally have no sewage treatment plants still. As in, their sewage goes straight from their houses into the rivers and the sea untreated, not because of a fault or undersized treatment plants or heavy rain ( all of which they have problems with too) but because the sewage system is literally designed to do that 24/7. The government was meant to have fixed this decades ago according to EU rules but has kept dragging its feet on building sewage plants. And they're probably not unique - they were literally the first country I checked, and the second, Spain, had the same issue as well.
I guess for me I just don't understand how nationalising a given company makes it stop emitting carbon.
What pressures would a nationalized system have? How about the fact that normal people don't want to ruin the environment around them? You don't need additional pressure to make sure that doesn't happen. If you stop optimizing for short term money the problem goes away.
And I don't give a shit about private budgets. The government doesn't need that shit, it can create money as it needs to allocate resources. And if it needs to reduce money supply that's what taxation is for.