I don't support stop and frisk because I think it's plainly unconstitutional. However, I don't think that the disparity of stops for young black men relative to their share of the population is necessarily the result of institutional problems.
All the different types of people in the world do not commit crimes at a rate equal to their share of the population. Poor people of any kind are more likely to commit a crime than better-off people. Men commit far, far more crimes than women. Young men commit more crimes than old or middle age men. There is, after all, that saying that the best thing to keep someone from being a criminal is a 30th birthday. Under stop and frisk, police are going to stop young men of any sort more often than, say, old women.
So you needn't address the racial dimension, because it's just a truism that young men, especially poor ones, are *exactly* the people police should be on the lookout for. Young men are the ones who commit crimes. Racist cops certainly exist and must be a non-trivial part of any discrepancy, but it's hardly determinative to prove serious institutional problems of the root-and-branch sort you're proposing.