Often, the DA will structure a plea bargain on drug or weapons posession (over a long list of more serious charges) because those are very easy to prove.
This idea that the prisons are full of good guys caught up in the system is detached from reality. Most guys doing hard time are guilty of about twenty other things that they haven't been prosecuted for.
Furthermore black offenders receive sentences that are longer than white offenders - http://www.wsj.com/articles/SB100014241278873244320045783044...
And white people are significantly less likely to be arrested for drug possession, despite usage rates being fairly similar - https://www.aclu.org/news/new-aclu-report-finds-overwhelming...
A prisoner deserves to be sentenced for the crime they were convicted of, not for any possible crimes that we think they may have committed. To behave otherwise is completely antithetical to a society that supposedly values justice
So no, prisons aren't "full of good guys", but they're full of people serving sentences that are longer than any rational policy would dictate who have been prosecuted in a system that has been shown time and again to have deep issues with bias and inequality.
Not to mention the violence and overcrowding endemic in the prison system. It should be a source of national shame that it has continued this long without real reform.
This is an oft repeated lie. Blacks use narcotics at well over double the white rate. Claims that rates are similar are based on surveys, as opposed to test data.
Anyway, you are missing the point here that prosecutors know exactly who they're convicting. Sentences now are almost all plea bargains. They get serious criminals to plea out on narcotics charges rather than go to court and face the full set of charges and a 25 year sentence. They don't even bother prosecuting some kid with some drugs. This is how the system works. It may be problematic, but it's not as broken as naive people assume.
