I self-identify as a neoliberal (fiscally conservative); is that part of the left?
Economics research says low wage immigrants are a net economic benefit, so it is in the interest of its citizens, but not completely objectively as some people are harmed. Also, I think the extreme poverty in parts of the world can justify help, just like how 1000$ is more to a poor person than a millionaire.
No, immigration alleviates poverty as Americans are much richer than the average person. Why do you think so many people want to immigrate?
I don't think it's a power grab by the left (open borders are not popular, as you can see right here) and that's irrelevant to the merits of open borders.
> the people who actually built the society that they want to invite everyone else to live in
This criticism seems to be for leftists.
Well, I am against forcing racial diversity, so you can stay with your ethnic group/society in my proposal.