I think there are 2 major points here we've summed up.
1. Marijuana is a source of income and jobs for the government (based on arrests/fines, confiscation, et cetra). However, we're creating victimless criminals, and also making the tax payers suffer from the confinement of non-violent drug "offenders".
2. Legalizing marijuana would hurt these government departments (police, etc), as well as, of course, the tobacco and pharmaceutical industries [*edit, and of course, alcohol!].
The only way I think you can go about making marijuana legal in all aspects is to somehow involve the government in making profit. You may also be able to accomplish some other things in the process/as a result.
The first step I think would be to form a group (much like this forum) and start growing and experimenting (much like this forum). But, in the long run, I think the goal would be to form a type of non-profit organization (this is only the 1st step). Eventually the government could step in and make profit from marijuana ONLY (I know, this is pretty shitty). But I don't know how else, conceivably, government would allow it to be legal without making money.
If government did make money (I don't now how much, for how long, or if eventually companies would form to reap the profits), you could also stop the people in jail, take the profits out of the streets...possibly reduce violence...etc. Just an idea.....
But maybe, just maybe, there is a deeper reason as to why it's been so hated on (besides the real reason, which I think, is because its simply been vilified so much throughout the years starting back when Harry J Anslinger did his best Hitler job [lied to his people] about the effects of marijuana).
One thing is for sure. $$$ WILL BE MADE. That's pretty much the only 100% sure shot.
**Edit, oh, and there also is the idea that you will create a lot more "upheaval", if you will, in society. People may want other drugs legalized (which I think should be the case - no one should have the right to force me to not put something into my body [with threats of jail or fines, etc), but they do have the right to say what I shouldn't put into my body and vice versa [through means of EDUCATION and truth). But in any event, this will pose as unwanted dealings from the powers that be.....and people will fear (the government will tell us this) that it will create more problems than good.