I don't think the author means that _every_ belief held by any person must ultimately become "objective" (and, therefore, aligned with that of all the rest of humanity). For instance, I don't see how it is bad for human civilisation if I think I look ravishing in red, whereas everyone else thinks I look like a pillock.
Luckily we dont need to know whether something is objectively true for it to be useful. And useful is really all you need.
The reason many people get scared when you answer these questions with "no" is that it would mean the complete decoupling of politics from reality. Debates about policy have a long history, and they're not harmful. But when one side starts also making up their own facts, it becomes impossible to reason, and a Venezuela-style decline might follow.
Logical reasoning with transitive trust networks could obviously be useful to re-establish a common reality. But while it might convince those that answered the two questions above with 'no' that the statistics are really compiled in good faith, no amount of reasoning will help with those answering "yes" to the first, and "no" to the second.
> However, in the long term it's detrimental to the stability of global civilisation when we hold and promote different and conflicting subjective truths.
If it's referring to "subjective truths" as identity beliefs, then yes, it could be an accurate statement. But if "subjective truths" is referring to more malleable beliefs decoupled from identity, then I'd say it's overstating things. Conflict that can be resolved with a positive outcome for all involved is better than no conflict, as a lack of conflict can lead to stagnation.