Edit: some of you take comments way too literally so for your benefit here is the exact question on form DS-160.
"Do you seek to engage in espionage, sabotage, export control violations, or any other illegal activity while in the United States?"
It's a similar idea behind the recent "Have you traded in any cryptocurrency" IRS question on tax returns. The idea is that it prevents anyone from claiming ignorance as to their responsibilities to disclose.
This isn't 4D chess, it's creating a reason you can detain someone once you know what they're upto without having to blow what you know about their real activities (which might lead to too many shutting down before you want them too).
This seems like a stretch. Any spy who gets detained for vague, amorphous reasons is going to assume they were detained for being a spy. Once you detain them, you have to hold on to them, and you've already revealed the fact that you suspect them. There's nobody out there going "oh look, they arrested our spy. Let's just leave everything out in the open and hope it was a coincidence."
Lying on official documents is an easy win which doesn't disclose technology and tactics. Its not apriori illegal to have worked for a foreign government's intelligence services - but it is to lie about it on official documents.
2. There is this national security risk with China. Just the other day, there was the top article on HN about a US firm having been hacked by China over a time period of years! This is not an isolated incident either.
3. Koreans like myself won't be denied entering even though we are same Asian race. We also have the mandatory military service, and have to mention it every time to enter US.
4. Nobody in the US California and New York calls it racism when you makes it harder for us to accepted to Harvard and Stanford because same test scores as Caucasians, we get dinged on the personality. This is a clear example of an actual racism.
5. China and Korea are both countries. Not races. NOT ALL Asians are Chinese. If I may suggest thinking a bit more before claiming to be on our side :(