What Sunny said. One of the most depressing things about the Labour leadership candidates' focus on The Very Real Concerns is that it enforces a deeply negative, ungenerous, and futile definition of what those Very Real Concerns are. If you're concerned about - to be brutal - the labour share of national income, and how it might possibly nudge up a tad, about housing, about unions, about green issues, you're out of luck. Your concerns are not Very Real ones.
These issues only get to the status of being Very Real if you can somehow work an immigrant in there. It's a circular process - the Serious People are only interested in Very Real Concerns if the Concerns concern immigrants. Why? Because only concerns concerning immigrants are Very Real Concerns that interest Serious People.
Of course, this is probably because it's hard to use a privatised immigration detention centre to build council houses. Once you've acquired certain skills, habits of mind, contacts, networks, etc, you will try to apply those solutions to everything. Part of the problem, of course, is that toughosity has a zero lower bound, a bit like the interest rate; there is no utopia of immigration detention.