Relatively speaking, pot is less "damaging" than alcohol and tobacco. The current trend to increase levels of THC is the natural progression in all agricultural endeavors. The higher THC levels may actually decrease some of the risks associated with smoking it (decreased inhalation volumes and shorter "hold" duration;
http://www.sciencedirect.com/science/article/pii/0091305789903699) and there is no conclusive evidence that pot is more harmful than tobacco with regards to pulmonary function. (Physiologic data were inconclusive regarding an association between long-term marijuana smoking and airflow obstruction measures;
http://archinte.jamanetwork.com/article.aspx?articleid=411692). That is not to say it isn't harmful to smoke anything, just that it seems no more problematic than tobacco, therefore trying to prevent its use by making it illegal is illogical when compared with the legal drug tobacco. More recent studies show some pulmonary dysfunction with heavy use but not with occasional use. This study also states that medicinal use "...is likely not harmful to lungs in low cumulative doses..." (
http://www.ncbi.nlm.nih.gov/pubmed/24384575) The fact that vaporizing is increasingly becoming the administration route of choice, it would seem that concerns on tar and "resins," and therefore pulmonary sequela would be further minimized. Furthermore, a brand new study, e-published in advance of the print version of Journal of General Internal Medicine, stated "Among adults in primary care who screen positive for any recent illicit or non-medical prescription drug use, we were unable to detect an association between frequency of marijuana use and health, emergency department use, or hospital utilization." (J Gen Intern Med. 2014 Jan;29(1):133-9. doi: 10.1007/s11606-013-2605-z. Epub 2013 Sep 19.)
In addition, THC has been found to be beneficial in many medical therapeutics, including PTSD (Drug Alcohol Depend. 2013 Dec 31. pii: S0376-8716(13)00524-3. doi: 10.1016/j.drugalcdep.2013.12.008. [Epub ahead of print]), seizures (Epilepsy Behav. 2013 Dec;29(3):574-7. doi: 10.1016/j.yebeh.2013.08.037.), and cerebral palsy (Rev Neurol Dis. 2007 Spring;4(2):103-6. Review, J Clin Pharmacol. 1981 Aug-Sep;21(8-9 Suppl):413S-416S.). Ongoing research suggest even more benefits could be realized. That is not to say smoking pot is without dangers, but when compared to other legal intoxicants, say alcohol, there is some evidence that it is less likely to be implicated in automobile accidents (J Stud Alcohol Drugs. 2014 Jan;75(1):56-64. Drugs and alcohol: their relative crash risk.). There does seem to be a positive correlation with onset of schizophrenia and psychosis, but even those associations are not well understood.
The point is not that pot is harmless, just that it is certainly no more harmful than other intoxicants that we as a society deem legal. That is hypocrisy. The other issue is that as free citizens, adults should be able to choose what to put into their bodies, be it tobacco, alcohol, or pot. The introduction of adulterants that could have adverse affects on someone, especially someone who is unaware of the addition of those substances, is another matter IMHO. It would be like adding LSD to someone's soda and not telling them.
The association between pot and violence and other crimes is most likely related to the circumstances these individuals must live when dealing in black market commodities. You do remember the effects of prohibition, right?
Is there an association between pot (and other drug use) and addiction? Probably, but does that mean that anyone who tries pot, as Reefer Maddness would suggest, is going to go ape-shit crazy? No. The fact that someone can smoke pot (Obama, Clinton) and use cocaine (Bush 2) and still become president (regardless of how you feel about Obama..) should be clear evidence that it isn't the boogie man the DEA and other government entities would like you to believe.
The bottom line, to me any way, is that it is difficult, and borders on hypocrisy and duplicity, to suggest that on one hand the government needs to get out, and stay out of one's personal life, be it their home or their choice to own firearms on one hand, and then suggest that the government somehow should insert themselves into an individuals life when it comes to the substances a citizen may wish to consume.