Racists are lazy.
There is no way around that realization. It takes some effort to view people as individuals and then weigh the good points against the bad points to make a determination about the quality of each individual. It is far easier to paint groups of people with a broad brush and take the individual assessment out of the equation. It is much easier to accept or condemn them as a group basing the decision on factors such as race or religion, or, for that matter, any of a host of other considerations such as income, country of birth or ancestry, level of education or any of a myriad of other subjective factors.
When it comes to race, that is a real easy one; it's as easy as distinguishing black, maybe brown, from white, no research necessary.