Can Marijuana ever be legalized?

yes, it may be legalized, but right now probably not because our president and congress won't cooperate

Also, there is general government inertia because we've had our "imprisonment for drugs" policy for so long, and some government officials are invested in it, or even have their jobs dependent on it.

Finally, there is rampant corruption of officials: they are paid by the drug lords.

But you don't have to have a conspiracy: never attribute to conspiracy what you attribute to incompetence, inertia, or stupidity. Sometimes, it just takes a while to get things done. Eventually, we may all see that the present policy on Marijuana is a bankrupt policy, and only makes things worse. And criminalizes normal behavior. The same mistake that we made for liquor prohibition, we are making for drug Prohibition, IMHO, but we may see the light eventually!