Examples of this in practice are the checkpoint around El Paso in West Texas that checks for all sorts of contraband. And the agriculture checkpoint on Highway 80 between California and Nevada.
In this analogy, Parler seems more like a single road used for lots of crime, while social media overall is the highway network that is more free.
Checkpoint cop, looks at people in vehicle, sees they are all white, bored sounding asks “is everyone an american citizen?”
Driver: “no, some of us are american and some are canadian.”
Checkpoint cop, confused: “uhhh that’s alright, proceed”
There purpose is supposedly to check for illegal cross border activity in the US and yet a car full of canadians doesn’t even blip their radar because it’s not actually about nationality it’s about race.
Which is all to say that i believe your comment about that checkpoint being about contraband glosses over the real motivations. In the dozens of times i’ve been thru there all i’ve ever been asked about is citizenship, and it’s never mattered what the answer is because i am white.
There aren't millions of Canadian citizens crossing the US-Mexico border illegally every year. There aren't tens of millions of Canadian citizens living illegally in the US.
They are trying to stop the 99.999% of illegal aliens who are from Mexico and Central America from crossing the border, not the random Canadian who is basically guaranteed to be entering legally.