* Highly skilled/educated immigrants provide a significant boost to economic growth and pay more in taxes than they receive in benefits. I don't recall whether the podcast addressed the impact of these immigrants on the wages of highly skilled native-born workers.
* Low-skill immigrants are a net positive in the long term (i.e., once their children grow up) to the economy as a whole, but their net impacts in the short term are somewhat ambiguous, and there is some evidence that they bring about wage decreases for low-skill native-born workers. While that evidence is not completely clear-cut, it seems likely that there's at least some level of impact. There's also evidence suggesting that some of the displaced native-born workers "climb the ladder" into higher-skill, higher-wage positions when this happens, which may mitigate that impact.
From what I've read more generally, my impression is that outsourcing has a much larger impact on unskilled workers' wages than immigration does, though I don't have a specific source to support that claim.
[0] https://ftalphaville.ft.com/2017/09/15/2193785/podcast-the-e...
[1] https://ftalphaville.ft.com/2017/11/10/2195727/podcast-kim-r...
In a magical hand-wavey manner where we ignore alternatives, obvious consequences, and opportunity costs.
They gloss over the reason they are considered a net positive is because almost everyone is.
For example their models will show that if the poorest Americans have lots more kids we will collectively be better off.
It’s pretty much just economists and the Catholic Church who believe it.