> This is a really terrible line of reasoning to pursue, because it's basically the continuation of colonialism - the need to have a caste of second-class noncitizens doing a large part of the work
Nobody said 'caste, second class or non-citizens' though. Yes, people who have the 'colonialist mentality' might assume that foreign-born people are only capable of replacing menial workers, but that's not implied by the basic logic that if people are born below the population replacement rate some countries and above it in others, some population transfer might be desirable and not consistent with much of the reality of immigration.
Unless and until deportation is eliminiated entirely, that's an inevitable part of being an immigrant. Regardless of the skill level and social status of your job. Even if you're a CEO you can still theoretically be deported for a driving offence in a lot of places, until you get your full permanent residence. And then you have to wonder whether a future government might remove that residence.
Aggressive stances towards deportation are the consequence of inaccurate arguments that immigrants are on average unwelcome freeloaders and destroyers of job value rather than making the future of the country more sustainable though. It's entirely possible for immigrants to have security of tenure and actually more desirable given declining birth rates: it's the assumption that our current society would be more sustainable in their absence which drives governments to make it as difficult as possible to obtain/retain.
All the rhetoric which drove repatriation of the Windrush migrants [a much more representative case than Begum leaving the UK to join ISIS] was based around the popularisation of the idea that the UK was 'full' of 'unsustainable' numbers of migrants. So it certainly doesn't help immigrants to pointedly refuse to state reasons why this is incorrect.
Nobody said 'caste, second class or non-citizens' though. Yes, people who have the 'colonialist mentality' might assume that foreign-born people are only capable of replacing menial workers, but that's not implied by the basic logic that if people are born below the population replacement rate some countries and above it in others, some population transfer might be desirable and not consistent with much of the reality of immigration.