I don't do drugs or want other people to do drugs, but still don't think it's my or the government's business if people do so. That's a textbook liberal position on the issue.
It would be equally illiberal to mandate that everyone do drugs or be polygamous. The illiberality is the imposition itself, not the quality of the imposition.
Despite many flaws, e.g. the Wars on Drugs and Prostitutes, the US is arguably still the world's greatest stronghold of liberalism (for the moment).
The War on Drugs is actually a perfect microcosm of how illiberal policy doesn't work. Instead of learning our lesson from the War on Alcohol, we doubled down and funneled untold billions of dollars into Mexican drug cartels via US markets — funding the very problem we wanted to solve. By contrast, our more liberal tobacco policy has been a huge success.