This one Doonesbury strip is just one example of politicians - mostly lawyers by trade - having decided that they know more than the scientific community. They now think they are more knowledgeable than the medical community, as well,. Much of the time, their decisions are religion-based, which should be - if it isn't already - against the intent of the Constitution which they swore to uphold.
This next illustration is to show just how useful the hemp plant could have been to the United States over the many decades, far more than the obvious recreational uses. Certain elements - political, industrial, religious - have been against any use of any version of the hemp plant, even though some have virtually no use recreationally. Even as more uses for the plant became known and proof was found that even the recreational variety was less of a threat to individuals and society as a whole than was alcohol, they stuck to their guns (so to speak) and refused to admit that they had wasted billions of dollars and lives on their so-called War On Drugs.
Of course, "they" also failed to realize that they could have made all types of hemp available and regulated and taxed its sale and made billions of dollars, if not trillions, by admitting their bias against a plant and its uses that they did not understand.
Here is a chart which shows the many uses of hemp, including its medicinal and recreational uses, but there are so many more: