^ You've honestly never helped out a mate who was outta smoke when you had plenty? I would find that hard to believe, I would say every smoker I know has done so from time to time and this does actually count as 'black market sales'. It's pretty ignorant to categorize all black market sales as the same, sure on the high end of the scale it is often reinvested into other criminal ventures but in other cases not so much. I have seen enough of the show 'Cops' to know it's far from unheard of to see 10+ cops kicking in someones door for dealing and recovering under an ounce of weed. I recall a specific occasion where a dude was charged with supply for having like two 8ths and a quarter packaged seperately, whether he was dealing or not I can only speculate but I know plenty of people (including myself) who don't sell who could have been caught out like that before whether it was due to seperating strains or just how their dealer sold it to them... If you think it is entirely in your hands whether you must participate in such activities as a Law Enforcement Officer I would highly suspect that you are mistaken, it is probably unavoidable in the course of a career.
Also, I feel that it's pretty bullshit you would book people for traffic offenses you commit yourself, what gives you the right? It's one thing for a parent or something to try educate their children to make better choices, but you are not better than any other member of the public. If you would do and/or have done that same shit yourself then where do you get the right to infract others for an identical offence?
I hope weed is legal in the near future too, and if it is likely to become so anywhere California is definately up there, however you can't hide behind this because it is far from guaranteed. Furthermore, I am aware this is cannabis discussion but your name suggests you use drugs other than cannabis, and I am curious if you see it as somehow more okay to arrest people for use or possession of these substances? Not having a go at you mate, just genuinely curious. We all make our own way in life and form our own morals, for me personally I couldn't do a lot of what being a copper entails (a profession that would otherwise be one I would perhaps consider and definately think would be exciting and rewarding at times,) without feeling highly immoral and like a total hypocrite, if you don't feel the same way then power to you I guess... I would urge you to think about the fact that if a cop had busted you for drugs it would more than likely prevent you from entering what is apparently your chosen career, you will be doing this to many you arrest for doing the same shit you have done.
As a side note I am jealous as hell of you folks in CA, down in Melboune Australia we don't even have MMJ.