Its been a while since I saw figures, but last I did domestic violence was at the top of the reasons people were sentenced to incarceration (that is, if you did a ticker at the door, it would be the most common reason) but narcotics were the most common reason people were incarcerated (that is, if you did a count of the currently incarcerated population, drugs would be the most common reason.)
The difference, of course, is length of sentence.
I don't think marijuana is all that high a share of those incarcerated for drugs, but if you are using the prominence of the reason people get incarcerated rather than the prominence of the reason people are incarcerated as your standard, you aren't looking at the right issue.
"the proportion of state prison inmates who were sentenced for marijuana-only offenses rose from 2.6% in 1990 to 3.6% in 2000"
http://www.aclu-wa.org/library_files/BeckettandHerbert.pdf
The DOJ reported that there were 1,236,476 state inmates in 2000 (http://www.bjs.gov/content/pub/pdf/p00.pdf). So 3.6% of that would be 44,513 state inmates who were imprisoned for marijuana only in 2000.
"King and Mauer (2005) estimate that at least 68,000 people were in prison, on probation, or serving a jail sentence for a marijuana offense in 2003"
So, that's 52% higher than the number I quoted for state prisons.
How many instances in a sampling size? How large was the sampling size? How rigorous was the study? Peer reviewed? Publisher?
Offhand, I can immediately tell you the overwhelming evidence is that tobacco (cigarettes) is far more harmful than cannabis. I direct your attention to the myth of cannabis being as harmful as x number of cigarettes[1] and the myth that cannabis harms brain cells[2]. While it does alter the brain, it is up for heavy debate whether it's harmful, especially on long-term use.
[1]: http://en.wikipedia.org/wiki/List_of_misconceptions_about_il...
[2]: http://en.wikipedia.org/wiki/List_of_misconceptions_about_il...
http://brain.oxfordjournals.org/content/135/7/2245
Of course, you could have googled this up yourself in 10 seconds but I guess people believe what they want to believe.
What about my comments appears as though I just look for self-validating information and ignore the rest? The parts where I questioned scientific rigor, sampling size, case instances, etc?
Depending on certain attributes that in practice cause one to end up in cuffs nonetheless.
In many major metro areas, you're more likely to be ticketed for cannabis than arrested.
I haven't taken the time to come up with a conclusive answer for myself on the extent to which cannabis criminalization imprisons people in the US; maybe it's as bad as people think it is. I just think it's worth doing some research on.