I can see how, looking at the whole thing purely calmly and rationally, that's easy to say. On the other hand, if you've spent 40 years building a life in a country, feeling like you belong, you've contributed to your new society, and built up a fair few assumptions around stability and security, then suddenly, out of the blue, to have the demand made of you that you prove your right to be here is going to be a bit of a shock.
It doesn't matter that it could be resolved with a 2 minute email - it shouldn't have happened in the first place, and is just another (OK, perhaps comparatively minor compared to people being flung in Yarl's Wood) way in which the Home Office is able to poison lives and create fear with, apparently, no second thoughts about the effects on those people. That, in my book, makes it pretty hard to justify.