People who are hurt by drug cartels. It is one thing to let people grow their own pot and sell it when they are law abiding (or otherwise law abiding) individuals. But when you get drugs from the drug cartel, the harm that goes into the production makes it wrong to use. We should support legal production and importation from human sources. But we should not legalize anything coming from the cartels.
That doesn't really follow. Nazi medical experiments were wholely unethical, but it would be completely unethical not use whatever knowledge they gained to save other people's lives.
Perhaps what you meant to say is that it would be wrong to pay for the drugs so the cartels actually benefit from their unethical behaviour. I agree with that, but that doesn't make the drugs unethical to use.
There's sufficient disincentive to conducting more unethical research by the simple fact that you'll go to jail. This wasn't a consideration in Nazi Germany.
We boycott and divest from companies for various human rights violations, why not boycott cartels?