If I put it in a Chinese context, spending North Korean lives to damage the US/Japan is also a good trade for China as long as north Korea survives. Kim could even die and it would be fine, as long as after the war North Korea is still there. Same for Iran and Hezbollah. Even if nasrallah is dead, we'll have to see what the end result is. Israel can only really win if Hezbollah doesn't exist as a serious force anymore after the war, which is rather unlikely unless they do a genocide
How hard is it really to do these assassinations in other countries? The Ukrainians did a few in Russia. Terrorist groups routinely do so. Israel just uses a lot of terrorist tactics when the US would use drone strikes and Russia would use poison. Is UK or German security bad because the Russians did assassinations there? When you can promise life in the rich world as a reward, you'll tempt poor people. I don't think Iran's security is particularly bad for its level of development, it's just that at this level of development this is the best you can expect. Israeli terrorists used to routinely kill Iranian nuclear scientists in the past. And yet, despite the losses Iran is now a nuclear threshold country and there have been far fewer assassinations than in the past.
Iran today has seemingly become immune to direct Israeli attacks, although Israel can still rope in US to help them attack Iran directly.
They're now a very different country than when they were isolationist. There is a weapons tech and industry pipeline going from China and even NK that is essentially fully secure. They're also importing more arms.
Russia can do the ultimate F you move and supply iran with nukes. I don't know why Russia hasn't considered that.
A nuclear Iran is not a good idea. China is banking on Iran as a bait for US, which requires US to directly try and invade. And US won't do that to a nuclear power. Secondly, if China acting through Russia normalizes the practice of giving nukes to countries to prevent US invasion, US can also motivate giving nukes to countries where China may want a future military solution, especially SK and Japan.
In the cold war, China's side is stronger militarily compared to US' side, so if the cold war is changed so that military forces cannot be used as easily (because of widespread nuke proliferation), China will experience more difficulty than US because of the changes.
