Well, you're in a tough position. (And I agree with you: I see no reason marijuana should be outlawed when alcohol and tobacco are not.) But I don't think you're likely to be compared to the Nazis. So you should let yourself off a bit. Still, as I said, you are in a tough position. I take it that deliberately not busting people for pot could get you in a fair bit of trouble, even fired.
Obviously, if you felt sufficiently strongly about this issue, you might find yourself with little choice but to quit being a cop. That'd be a tough choice to make, I'm sure. So I wonder if there are alternatives.
To what extent is it possible for you to speak out on this issue, given your profession? The issue of mandatory sentencing is a very important one here. Could you speak out on that issue?