Another example of why the "just do whatever the cop tells you to do, and you'll be okay" philosophy has some serious holes in it.
Many probably did not, a few might have and been legitimately innocent and had stuff planted on them. Innocent or guilty overall, if their case is based on a cop planting evidence on them, they should be set free (and sue for whatever they can get). Just out of curiousity, what percentage of people in prison do you think are factually innocent of the crimes of which they were convicted? Would the rest not have been better off not committing crimes? Your advice, to heed my advice, is good advice, and should be heeded by everyone. Take heed people. Don't commit crimes. Don't have unprotected sex. Statistically, your life is much more likely to improve.