To be honest I think the number of men willing to commit violence (and usually die in the process) has always been quite small. Even Medieval armies often only consisted of a few thousand or rarely tens of thousands of men, often forcibly drafted, from populations of hundreds of thousands or even millions. I do agree the main thing stopping mass violence is because Western governments have powerful militaries that can stop it. However, if the society weakened, and vacuums opened up, there would be a significant enough number of men who would commit violence and fracture the society, Mexico is a good example of this, it's a semi-wealthy society, it's not dirt poor and far more richer than any Medieval country would have been, but even there under only semi-anarchic conditions, you have huge numbers of men fighting and dying in those cartels, both against each other and against the government. Since 2006, 250,000 people have died in that drug war alone.
In my opinion, I think Russia views the West as an existential threat. Because the West has heavily pushed for democracy and regime change which has collapsed fellow allied governments in the Ukraine, Georgia and other countries previously, Russia has become paranoid of the West. Even during 1980s in the Cold War, the Soviets were ready to use nuclear weapons in weeks in case of a conventional conflict with the West, so I don't believe that current-day Russia is interested in preserving the West in any form. Hence, their support of the far-right and far-left makes sense in this context, as it greatly harms Western society, and could possibly cause a Western collapse in the case of severe infighting.
In terms of casualties, I would agree that both domestic and foreign terrorist attacks on their own do not really do any damage. However, it's people's overreaction that does the damage, especially of the far-right, which fuels the far-left. And this causes riots and further instability. I think this is why the West is very aggressive in going after terrorism, even to the tune of spending trillions in hopeless wars.
Very true, I do think it will be ultimately a Malthusian future that does us in. Our massive consumption of resources is destroying the planet, and as the rest of the world also heightens its consumption and population levels, it will cause even more damage. We are already past the threshold where the catastrophic damage of global warming could be averted, and we are on track for a world 5-6 celsius higher in 2100. Our emissions are not decreasing, and are still growing rapidly, so this will cause profound changes in the world, such as the loss of the ice caps causing global flooding, the destruction of many carbon reserves releasing more greenhouse gasses in the atmosphere, mass die-off of oxygen-producing algae in the oceans which make up 70% of our world's oxygen production, etc.
