The problem with discussing “concerns about immigration” from a left wing perspective is that it involves the immediate assumption that immigration itself is a concern or a problem - and this already frames the debate in a way which benefits the right wing, and allows them to stir up fear.
Objectively, immigration is simply a fact of life amongst migratory species - to say it is a “problem” is like saying wind is a problem, or the tides.
That said, it is necessary for the left to have a line on the issue. Whether we like it or not, it has become or perhaps has always been a primary concern for many people. From a working class perspective, I do not know if these fears are more prevalent amongst this class than in the other classes, but I do know that many working class people have strong concerns about immigration, rightly or wrongly. Obviously, the left wing is traditionally rooted in a working class base, so again, it seems foolish for the left to simply ignore this issue in terms of debate, as sometimes seems to be the case. Not only is this dismissive of the concerns of working class people, but strategically it surrenders the issue to the right.
I think the thing that the left misses is that some forms of immigration, if not a problem in themselves, are at least symptomatic of a problem or problems, and many people sense this.
The first problem that immigration is symptomatic of is simply the huge inequality that is maintained by global capitalism. As long as there are parts of the world in which opportunity and wealth is far more freely available than in others, then people will desire to move. Globally, the fact that there are so many places where people are forced to migrate, because of war or famine or both, is a serious problem. Of course, in this problem, the migrants are the victims - a fact which the right chooses to ignore or invert.
The other problem which I think many people correctly sense is not so much about immigration as about population. Obviously, as with Malthus, fears about population growth can be unfounded and can be used to demonise sections of society. But it is also true that capitalist nations do benefit from constantly growing population. In fact, under the current model, they rely upon it to generate ever increasing GDP. Clearly, this is environmentally unsustainable, and people instinctively know this.
I think the immigration issue ends when we as a society learn to distribute wealth and resources with a stable or even declining global population.
Finally, and I’m just thinking aloud at this point, but I do sometimes wonder if people simply have a right to decide exactly how dense they wish their local population to be - especially in places with limited space, such as islands. Qualitatively, the amount of people living in close quarters to you does affect your life - in terms of space, in terms of pollution, in terms of social environment. Personally, I enjoy living in dense urban environments, but many may not.
These are what I think could be deemed the legitimate “concerns” with regards to immigration, whilst trying to think charitably towards those with concerns. Of course, many on the right may be arguing in bad faith. Also of course, it benefits the capitalistic class to sow enmity amongst the working class, and to blame the material inequity inherent in state capitalism on something as simple as immigration. But I still think the left needs to talk about immigration, and to talk about the global problems which necessitate it, and to accept that there are indeed problems - but to identify that these problems are based on global inequality and the need for infinite growth.
TLDR i have no solutions