The original intention is irrelevant for today. If a good law was originally passed for racist reasons that is no reason to abolish it. (Not saying that drug prohibition is good.)
> Today, those policies still affect blacks and Mexicans more than whites, even though drug usage is similar. Therefore, the policies are still racist.
Just because a policy does affect a certain group more doesn't mean that the supporters of the policy are against the group. For example, Blacks are more affected by laws against murder, but that doesn't mean that those who support laws against murder are racist.
> Today, those policies still affect blacks and Mexicans more than whites, even though drug usage is similar. Therefore, the policies are still racist.
Just because a policy does affect a certain group more doesn't mean that the supporters of the policy are against the group. For example, Blacks are more affected by laws against murder, but that doesn't mean that those who support laws against murder are racist.