You really don't want to be in that early oppressed group.
IMO, it's because human systems are over-systematized and over-regulated. It always causes oppression. Some group of people has to pay dearly for all the structures that are imposed on them. Laws and social structures essentially never work for everyone equally; at scale, many laws systematically steal wealth, power and opportunities from one group and give it to another.
Even the most well-meaning laws basically end up stealing from certain groups of people for the benefit of others. Especially on a complex global playing field. Just look at Africa. It's not their fault that they're stuck in poverty... Western powers keep installing corrupt dictators by sponsoring coups. The dictators then saddle their citizens with debt. The people have little say. Then basically they become so poor that they are forced to immigrate to the rich countries which are causing the problems... And for the most part, join the lower class of that society where the oppression continues under a different form.
They get to be oppressed in this slightly different way while also contributing to the continued oppression of their people back in their home countries through the gift their cheap labor to their oppressors in their new country, which enriches them. This is made possible by a combination of ignorance and intergenerational low self-esteem inflicted upon them by their oppressors as a result of manipulation of the political systems of their previous countries.
IMO, US leftwing politics are extremely short sighted with their approach to immigration because they are building a critical mass of oppressed people in the US. Some people will be grateful initially but the gratefulness will soon turn to disdain once the new reality sinks in.