I don't doubt that the Nixon administration exploited the war on drugs for nefarious ends. However, I think the idea that the entire impetuous behind it was to target particular social groups is bordering on a conspiracy theory. It is a bit like suggesting that Democrats are pro immigration only because immigrants tend to vote Democrat. I'm sure it hasn't escaped the notice of Democratic electoral strategists that the party could stand to benefit from immigration. But it would be implausible to suggest that this is the only reason that Democrats tend to favor a more liberal immigration policy than Republicans.