I got a light interrogation as a US citizen. For the record, I have Global Entry, NEXUS, and TSA Pre-Check.

I handed the border agent my US passport and the conversation went like this

"why are you entering the country?"

"I live here"

"do you have legal status in the US?"

"I'm a citizen, you're holding my passport"

"have you ever overstayed a visa in the US in the past?"

"I was born here, so no"

"do you intend to do any work while you're in the US?"

"yes, I'm a US citizen and I have a job"

I didn't get pulled off to the side or anything, it was just standard questioning at entry processing when flying in, but it was just bizarre

the border agent kept looking me up and down suspiciously like I was hiding something, but he had my passport the whole time

even when I got questioned on my way to Canada (I would've stopped me too), they were much nicer about the whole process, it's an air of "we're just double checking cuz making a mistake here would be real bad, but as long as everything's legit, no worries, I hope you have a nice stay in Canada"

entering the US the vibe is "you're a violent criminal and it's my job to ask you questions until you slip up and admit that fact, the US is magnanimous for allowing you to touch our great country's land with your disgusting feet, and you should remember that every day you're here or we'll detain you so you won't forget again"

I'm a little surprised you've only had positive experiences.

That is indeed quite bizarre. Most of those questions literally don't matter for a citizen, and if you were somehow falsely claiming to be a citizen, the other questions also don't matter because a false claim to US citizenship is punished more harshly by US immigration law than the other things they were worried about. (Such false claims make one permanently ineligible for permanent immigration to the US, with no waiver available, and require a waiver for any kind of nonimmigrant admission.)

> I'm a little surprised you've only had positive experiences.

I was talking about the experiences within the country. The border is horrendous, exactly like Russia. Same vibe of "we hate you, kneel before stepping into my country"

For a foreigner, even one that knows the US pretty well, there is a background feeling of "if it goes bad, it will go vey bad". This is mostly because of movies and news like this article but the everyday life was more or less friction free. I did not get into anything serious, though.

Are you flying or driving? These were at land borders in Michigan, maybe they're more strict when you try to bring in a whole vehicle instead of a few suitcases that have gone through inspections.

YMMV on so many factors. Which border, how you look and carry yourself, your vehicle or airline, etc.