First of all, if you write your essay or paper on this topic, you will want to be careful about using the term “American ideal” for a certain type of look. Be sure you introduce the term and define it in such a way that it is clear that you are not saying that people who look wrong are not ideal Americans.
As to the substance of your question, the best way to refute this argument is to look at actual data from crimes. First, you will need to define what your “American ideal looking” person is. Then you will have to look at crime data to see if such people are really committing more crimes than they once did. You will need to pick some starting point with which to compare the present. You will need to look at the trends in crimes committed by various groups of people. Be sure that you compare this with their proportion of the population. You need to look at crimes committed per capita among that group so that you do not simply conclude that the group with the most total number of crimes is the most likely to commit crimes.
If you find that your “American ideal looking” people have not been committing more crimes per capita over time, you can at least tentatively rule out the idea that criminals are recruiting ideal-looking people to commit crimes for them.