I eventually went to look at those studies. That's because I was a legal immigrant to America, and I knew the process of immigration very well. I have also been the legal resident of multiple countries on three continents, so I'm familiar with this.
Those studies are dishonest. What they don't tell you is that legal immigrants certainly do better than legal residents. What they do is not differentiate between legal and illegal immigrants. Sometimes, they mix they two, with the majority being legal, so it skewers the results.
The bottom line is that, in Europe now, borders are closing because they have discovered that 'immigrants' bring some bad habits with them. In Ireland, the UK, and virtually every country in Europe, there is a huge outcry about the crime.
In the UK, the government will not release figures on which groups commit the most crime. They withhold all information from the public. Why? The probable answer is because it will prove once and for all that it's a myth that illegal immigrants don't bring crime with them.
It's interesting to read those studies. I'm glad I took the time out to do so.