Having said all that, he never had a choice to begin with. When Google decided to stand up to China, they didn't bet the farm but "only" a lower double digit percentage of their revenue (my hat's off to Google for that). Apple cannot produce their hardware anywhere else in the world at the scale and quality level that they are currently getting from China. I am saying this as someone who has a good amount of insight into how the Chinese production capability compares to other parts of the world.
His fiduciary responsibility was to do what's best for the company. If he stepped down, it would have taken no time to find the next guy who would have happily done what's best for the company (except less well). So really, it's entirely inevitable.
If you buy into the last sentence, you might want to ask yourself what the long-term future of a capitalist society looks like when it's economically attacked by a very capable totalitarian regime that can think strategically rather than being beholden to the capital markets.