Yes, humans still provide value. Correspondence chess players will for example read chess opening books to find if there any mistakes in that book and even if they find just one, they'll try to lead their opponent into that dubious line, which is often a mistake that computers can't easily spot. Also as a former highly-ranked chess player, I'd use multiple chess engines at the same time to compare and contrast and also I'd know their strengths and weaknesses and which possibilities to explore.
Anecdotally this feels very true. Those outside of the AI community feel way more optimistic than those I know who work in AI. The general population who are aware of GPT and LLM's seem way too optimistic. When I talk to people about an AGI capabilities moratorium, AI researchers are way more likely to agree than those not working in AI.
Just because good behavior is contagious doesn't mean it will necessarily spread. There are people and/or organizations that purposefully want to troll or be bad actors either for monetary gain (false short report to manipulate a stock price), political gain (foreign interference in an election) or out of their enjoyment or possibly some mental disorder or to show off or enjoyment of breaking norms. A rational discussion or showing good behavior might not be effective in stopping the intolerant speech or behavior. So just displaying good behavior in response to bad behavior doesn't always solve the problem and sometimes the bad or evil actions need to be fought and/or not tolerated. In terms of hate speech, I've noticed that often people that conduct hate speech don't want to engage in rational discussions and a lot of the hate speech on social media is generated by bots. That intolerant hate speech then might become contagious in a negative way!
The book claims that authority by government is never justified and you state also that private agencies are expected to outperform the government. I take issue with both of these claims. Free markets fail to solve tragedy of the commons problem for which collective solutions through government are the best solution. Free markets also often fail in solving inequality, externalities, asymmetry of information, monopolies and the free rider problem. A world under anarcho-capitalism would likely lead to a large monopoly by a powerful force controlling security and weapons for which life for the average person would be worse than our current system run by democratic governments. Countries with higher amounts of government spending have higher levels of Quality of Life after adjusting for level of development.
Aging/longevity is likely one of the top problems facing humanity especially when it seems possible to solve aging within your lifetime, so would add that to the list of topics to study. Also the rise of social media and in general the increase in the instant pleasure industry is having a huge impact on humanity so a topic worth exploring.
When looking at polarization in the US, it's more at the Congressional level than at the presidential level and this is often due non-competitive general elections so the winner of the primary will be the winner of the general election. This has gotten worse as gerrymandering has continued to increase. In more competitive races, you see the political parties trying to select more moderate candidates.
Conspicuous consumption luxury spending is not a good use of resources and is a negative externality. Some spending is very beneficial such as that on basic research or demand for healthy goods which leads to more production of that healthy good. Spending money on something signals that their is demand for that good or service so leads to more production of that good or time spent on that service. Society would be better off with more medical research and less yachts and JPEG NFT's so we want to encourage spending on health instead of some luxury goods.
More humans leads to more knowledge. There will be more people doing basic research and adding to humanity's collective knowledge which will improve collective wellbeing. There are efficiencies of scale as someone else mentioned and in the book Scale the author mentions productivity in cities scales 1.15x superlinearly with population. There is an upper limit, though the current population growth rate is well below the peak and very likely a much higher growth rate than today's can be sustained.
You claim lockdowns are almost certainly net negative but plenty of research papers on the cost-benefit analysis of lockdowns come to the opposite conclusion. Lockdowns saved plenty of lives, prevented long Covid and stopped hospitals from being overwhelmed at the costs of ~5% of GDP and decreased mental health. I could see that for certain segments of the population such as young people that lockdowns are a net negative, though a large decision like lockdowns should likely be decided based off the benefits to all of society and for older people lockdowns were definitely a huge net positive.