A lot of people, and a whole lot of liberals ;-) , don't understand that just because you can do a thing, doesn't mean you should. Colin had the ability to kneel. And he paid the consequences of his choice. It is the natural way of things.
That is a good and simple insight on the reality of life. We see pretty much eye to eye. It
is the natural way of things as they currently are. You can't argue with reality!
A lot of people, and a whole lot of conservatives ;-) , don't understand that just because you can do a thing, doesn't mean you should. Trump had the ability to campaign on the promise of a "great, great wall" to keep out "rapists" and "criminals" (who are known to be hard-working honest people by a large percentage of the US population). And he is paying the consequences of his choice. It is, indeed, the natural way of things.
There is no need to debate whether Trump is racist or not. In the end what matters (and the answer to your question) is whether people think his wall is a racist artifact. In the end that is what matters! The bottom line is a large percentage of people believe it is.
So people's morality did not change, it is Trump's presentation of the wall that made it immoral in the minds of so many.
You may disagree, but this is the answer to your question of how a barrier at the border became immoral.