It is relatively easy to persuade people to follow a leader, or agree with a very bad idea. Our prime example is that Hitler was an elected leader, and his policies of enslaving or executing Jews, gays, black, and cripples were the legal policy of the government. The people supported his party in the elections and continued to rally behind him as he began his conquest of the world.
The idea in the US is that government responsibility is in three parts that balance the fairness and justice of each other. The courts are guided by established laws and traditions, and when all else fails to resolve differences they refer to the constitution. State "Supreme Courts" are goverened by the State Constitution and the Federal Supreme Court is guided by the US Constitution. Even laws passed by congress are subject to this kind of oversight, and just because one political party might decide that, for a silly example, that "mashmallows are a danger to the security of the state" and therefore no marshmallow companies could continue to operate, passing a law to enforce this believe, the courts could (and should) reasonably decide that the law is not reasonable.
The general sentiment among a large number of people is that most of the drug laws are unfair and unfounded, but there is sufficient legal history and conservative support that people passing laws legalizing the use of marijuana for "health" (medical) reasons may not be "constitutional" (according to the particular state's constitution) because it would violate federal statutes or regulations.
Is it always what we want to see as an outcome, that popular issues are voted on by people and the courts "reverse" the will of the people? No, of course not, but this is also why we must pay attention to our politicians' attitudes on the issues so that the judges appointed to the courts (ESPECIALLY the SUPREME COURT of the UNITED STATES) will be those most likely to agree with the attitudes of those who appointed them. Should there be "proof" that they will rule in a particular way? No, I don't think there should but if you can rely upon them to look at each case fairly and have a general outlook that agrees with you (or more specifically the politicians you elect) then the court decisions are more likely to be ones that you agree with too.
love
Stafford "Doc" Williamson
make it a greener world, support "waste to energy" programs like those from http://winfotech.com/energy/daochi-energy-brochure.pdf