A huge number of people are in jail for commiting violent crimes that while not labled "drug related", are still related to the war on drugs. Drug prohibition funds gangs and cartels, which directly leads to a host of other crimes.
If you ended the war on drugs, it's likely that the prison population would drop by much more than 20%.
I'm not sure that's a given. Ie once drug trade loses its profitability, I expect the individuals involved in it to move to something else (but hardly to other poorly paid jobs requiring commensurate levels of education).
Ie - did ending of prohibition bring the end of the organized crime?
[1]A widely repeated claim is that, as a result of Portugal’s decriminalisation policy, drug-related homicides increased 40% between 2001 and 2006. But this claim is based on a misrepresentation of the evidence. The 40% increase (from 105 to 148) was for all homicides, defined as any 'intentional killing of a person, including murder, manslaughter, euthanasia and infanticide' – they were not 'drug-related’
That document pretty explicitly says it has no idea if the statistic is linked to drug policy.
However, even if we posit that the correlation is significant, I'm not sure what you can read into this. While comparatively enlightened, Portugal did not legalize drug possession and didn't decriminalize vending of drugs. So organized crime is still the one making (and fighting over) all the money.
To this day, the best example of the social effects of repealing prohibition is the repeal of Prohibition.
If you ended the war on drugs, it's likely that the prison population would drop by much more than 20%.