Has more suffering and death occurred in China before or after China opened up to the rest of the world? If they remained closed off to this day, they would much more closely resemble North Korea.

Before, for sure, Mao policies were pretty ruthless.

Actually it's quite easy to predict! We can simply look at the track record of Western intervention since WW2, see that it comes down so squarely on the side of "please USA just leave the world alone, my god" that it achieves the platonic definition of a square, then call it a day.

Why exclude WW2?

I'm assuming you're saying this because you want to compare China to Nazi Germany, which is strange when the USSR is a much more apt comparison that existed in the postwar period.

Maybe you shouldn't assume. Maybe you should take Rebelgecko's question at face value, and actually answer it. If you're going to claim that the rest of the world just wants the US to leave it alone, why exclude World War II?

I'm just curious about people's reasoning whenever they cherrypick arbitrary start/end dates

WW2 marked the birth of America as global superpower, as it was the only developed nation to have its infrastructure basically untouched by the war.

Why do you think so? China is acting very much like Nazis in many cases. That they both call themselves communists doesn't mean much, actions matter.

There are parts of the world like eastern Europe that would've liked US intervention, on the other hand.