Actually, this current push toward "open borders" wasn't part of (yes, what I call) the "left" even ten years ago, was it?
Don't even know what you're talking about... There is no push toward "open borders" rather the contrary. More and more people both from left and right ask for closed borders, especially in free moving areas like EU. I don't know all programs of all political parties of all countries but in mine the left is heavily against current state of the EU and ask either for a huge change or a Frexit.
It's recent and there are specific reasons why. Ten years ago, it was part of a group of concepts being pushed pretty much only by one Soros funded organization.
Again I don't know what you talk about. EU is a project of open borders that was heavily pushed forward something like 30 years ago and is heavily questioned only now...
And why exactly do you think today you have to believe in that idea? I didn't use the phrase "goose stepping" without some reasons, you see.
Irrelevant as you absolutely never proved in any way that "the left is pushing for open borders".