I think this is an important message, even if we are going to be optimistic about the future. We need to move away from a sort of assumption that no matter how difficult things get, we will survive in the end and somehow it will all be OK. It’s incredibly frustrating to see people who will still not admit that we will soon have a serious problem with getting energy from fossil fuels, or that climate change is real and will have devastating, long-term consequences, or that we can’t just keep growing indefinitely, or that the things we feel we need or want are not necessarily our right to have, and may not be around for that much longer. In the 70 years since WWII, we have gone from using minimal fossil fuels to almost exhausting them - and we aren’t even slowing down. We have found ways to be more efficient and refined other renewable but somewhat limited sources of energy, but as in the link @tekna2007 posted, this has not even come close to replacing fossil fuels or building a sustainable future (which I would define as being a lot longer than my own lifetime). Evidence needs to be presented that we can control our consumption and switch to renewable sources, because the data is shouting otherwise pretty loudly. Now countries like China are really starting to consume on our level, and there’s not a whole lot we can say against this growth without showing up our own hypocrisy. The best thing we can do at this point is move away from the idea that we will somehow find a magical source of energy that will solve all of our problems - at this point, it isn’t looking likely. “Sustainability” is a lie, for the most part, and has been co-opted by consumerism to make us think that buying green is actively helping the planet, rather than hurting it a bit less than if we weren’t being environmentally friendly. This isn’t to say that environmentally aware products aren’t good, but consumerism and capitalism aren’t going to save us and leave us with everything we had before.
I don’t think Kingsnorth is claiming that we should despair absolutely, just that we should face the facts and redefine our parameters for success to remove our wishful thinking and survivor’s bias. Civilizations have been wiped out before through lack of resources, so if we can’t even imagine it could happen to us we will be fatally unprepared when it does.