I think what should be important to conservatives, is whether or not what the federal gov't did in making pot illegal was Constitutional. Otherwise, conservatives who support keeping pot illegal no matter what are no better than "end justifies the means" liberals who force their own opinions on others via the courts.
Don't underestimate the emotional attachment some people have to the subject. Some self described "conservatives" will defend the New Deal to justify the government's actions, and willingly hand over the means to the liberals just to have a little piece of it for their own use.