Its unlikely that i will ever be carded - not because I am white, but simply because i do not hang out in dubious places late at night. The fact is that there is a much higher probability that those that do so are involved in some form of illegal activity and there is a correspondingly higher probability of them being carded. 
If a disproportionate number of minority and immigrant youth place themselves in this position, it is a social problem and it is unfair to blame the police for something which is not within their control. They simply have a job to do to protect all of society as best as they can.