Let me play the devils advocate. There is the human right and freedom of speech. This includes the right to complain, despite the hypocrisy.
Perhaps their "conquering" was a sort of European mob mentality, a sort of international keeping up with the Jones's. Everyone wanted a piece of the pie.
Yes they exported their language and perhaps parts of their culture to most of the places that fell under their jurisdiction. But does that give the underlings any right to mass migrate to the head nation?
The immigrants also take a lot from "their economy". For instance, many people form destitute backgrounds or marginalised groups in their countries of origin, now have the luxury of a good career and home ownership. Something they could only dream of in their own native lands.
Often times these "stressful labour" jobs are small companies run by other ethnic minorities exploiting their own people.
Sikhs faced discrimination from a tide of Hindus on one side and Muslims on the other. Now they have an equal footing in a country that allows them to improve their standard of living. Moreover they have the right to practice their religion in relative peace, and their religious customs like special daggers, underwear and turbans are respected and acknowledged by the government in the UK.
Basically your argument: cultural enrichment for thee but not for me.
The Uk have colonised the world mainly for exploitation reasons only.
They knew other countries have great resources. In the medieval times Europe were broke and filthy and diseases were heavily ridden everywhere.
In the times of the industrial era: they knew they need labours. The natives wouldn’t do the work that required heavy stressful labours.
It’s why they knew countries that are poor that comes from a lower economical background are the right people to use for the job.
Racist pseudoscience are also the reason why slavery have continued.
But thankfully that have stoped.
The native average white bloke with a bulldog tattoo, doesn’t know what his powerful leaders were up to in those times of that era.
Sometimes they still don’t know but they want them out because they’re not
yt.