You had me until this paragraph. You’ll be lucky to find a country in the world that doesn’t have some form of Immigration control!
Now, in 2021, yes. It wasn't always - it began in many countries, including the UK, as a way to deal with influx of refugees they found undesirable a bit over a hundred years ago that has creeped up more and more over the years and many countries have followed those examples. There were other methods of population control and deciding who is a citizen, but 'immigration control' is a recent development historically and socially. Now we have countries, starting with the US, that want to monitor the bank accounts and going ons of citizens who leave -- like the previous analogy, it's like a really bad ex who won't leave you alone.
It's a government power that they can through force enact, but discussing it as a right puts it into the same realm socially as the right to a fair trial (while the UK has indefinite detention centres) or the right to freedom of expression. I'm wary of anything that puts the government or any social system's power in the same way as we discussing hard fought for individual protections, because the former is often used to ignore the latter. Power will do anything to make itself seem justified.
It's not fair to EU nationals to just say, well that's how immigration works. It's not how things worked when they moved here and lived here all these years.
This is also true of non-EU national residents. I got ILR in '06 - Life in the UK test didn't exist. BRP didn't exist - once you had ILR, you were done and safe, now that's changed too. Now we have to keep proving our residency and pay to regularly update our biometrics and there is a really odd issue that while BRP are meant to last a decade, pretty much everyone has the same expiration date on their card because apparently the technology in them won't be good anymore after the 31st of December 2024. I got my most recent BRP last February, same date on it as the one I had before -- and get this, they're still trying to blame the EU for it even for cards that came out after we left, even after they raised the price and brought in "private partners". It's ridiculous.
Didn't think in '06 that I'd still be paying to keep the rights that I was meant to have 'earned' that year with my ILR. That wasn't how things worked and we're not as psychic as some like to think we are. I've lost count of the times I've been told I'm not allowed to complain because, as a non-EU migrant, I "knew what I was getting into". Everyone's being fucked over, it's not an honour, it's a racket but for now, we've got to deal with it.