(disclaimer, I have donated to BLM causes and don't consume Fox News)
I think you have you answer in there - anyone who watches/reads Fox News or similar thinks that BLM is something very different than you think it is.
You can choose to write off anyone in the world who watches conservative TV, but you can't call yourself welcoming for doing so.
> Why would a non-US visitor feel unwelcome seeing that?
As a non-US visitor with some knowledge of history I am extremely put off by the banner supporting an extremist communist organization, like it is nothing. Just have a look at their original manifesto that is now removed from their website (wayback machine has it).
Why would a non-US visitor feel unwelcome seeing that? Why w
And as far as it being a political message, that's also a matter of branding. It's been actively demonized by one particular party, whereas most of its supporters likely consider it to be apolitical -- simply about social justice.