I hold a passport from a country whose citizens do not need a visa to enter the US and can spend as long as 6 months in the US legally without a visa. That said, I know that I am subject to being turned away at the border for any reason because I am not a US citizen and I do not have an absolute right to enter the US.
What part of this don't people understand?
They've had 8 or more years' administrations that turned blind eyes to enforcing the laws on the books.
One grows accustomed to laxity, and comes to believe it's the new normal. Then, when enforcement is restarted, they yell and scream that it's unfair.