Simon... but they are still additional crimes, with victims that otherwise wouldn't be
Assuming the conclusions from the Pew study are reliable,
If most illegal aliens are presently employed, but later removed, then the crime rate will go up once they are replaced by a cross section of the population or legal immigrants.
If they are not replaced and the economy shrinks instead, you still have a higher crime rate than before the removal of illegal aliens. So your argument doesn't hold.