I agree that "We must work hard to convince people that drug prohibition is a folly: harmful, ineffective, counterproductive, extremely expensive, and morally wrong" but that doesn't preclude pointing out the existing legal protections afforded by the "religious freedom" that we're supposed to have (even if we don't), and the fact that Cannabis IS an "herb bearing seed."
If "We can't attack drug warriors with arguments based on the meaning of words" then words lose their meaning. I think it's important to respect the meaning of words, even if no one else does. The legal and pragmatic distinctions need to be made by us or, as you suggest, they won't be mentioned at all. All arguments are relevant as a part of a comprehensive rationale.
In the interest of peaceful discourse, I think it's important not to characterize what we do as "attacking drug warriors." I prefer to reason. to educate. I seek to understand and find common ground with people who are reasonable.
"Drug warriors" who refuse to acknowledge compassion, science and reason can be disempowered by legally and logically convincing people who are truly concerned with solutions to problems being created by prohibition.
To this end, one indisputable distinction between drugs and herbs is that herbs grow from the soil, drugs don't. This brings up obvious differences in the possibility of "control."
Another difference is that drugs are more concentrated and homogenized than herbs. This makes drugs more dangerous than herbs. Public safety is a legitimate concern, that favors the freedom to farm.
Finally, herbs are a product of nature, a gift from "god." In debating prohibition with people whose thinking is often oriented toward "religion," this argument may carry more weight than logic. Herbs are a fundamental right, at least in theory, protected by international treaty.
Ofcourse hypocrisy exists in the drug policy debate, but that doesn't mean we have to go along with it, or have what ought to be a legitimate legal argument derailed by it.