The war on drugs was instituted as a racist policy [3]. It's quite likely that the main motivation here is using drug laws to punish people of color.
[1] http://www.slate.com/articles/news_and_politics/history_less...
[2] https://www.theatlantic.com/magazine/archive/2001/03/getting...
[3] http://www.cnn.com/2016/03/23/politics/john-ehrlichman-richa...
If the federal govt. has to enforce federal law in a state, that needs to happen, and the state needs to cooperate to the extent laid out by statute & legal precedent. No more, no less.
The right answer is to have legislation that squares the federal & state policies at the top. "States Rights" never extended to nullification of Federal law, there was a substantial dispute over this in the 1860s.