Not sure whether to join in at this particularly bun-righty stage but this is an example of a very unhelpful view point and where some of the "anti expert" sentiment (which I don't think is really this) expressed around the ref comes from.
I posted above a reasoned response to saying WHY concerns about immigration are not really valid
No, you didn't. You quoted a couple of studies which looked into a narrow aspect of the issue. It's not how research works, that one study is done and then the issue is closed. Studies need to be replicated before they can be accepted as reliable. Also these studies will have been based on certain assumptions which not everyone might agree with. Also the studies will be within certain parameters, which again, are open to debate.
So people who say they do not always want experts telling them what is correct may mean that they disagree with the assumptions which the expert is using, or with the parameters of the subject.
Immigration, or any social/economic issue, is a very complex, multifaceted issue and is constantly changing. To say, no concerns are valid because of one or two studies, with all their assumptions, limited parameters etc, is not helpful. I expect even the authors of the studies would not draw the sweeping conclusion from them that you do Small - that we now know everything we need to know about the effects of immigration and don't need to consider it any further.