The use, growing, or consumption of the drug marijuana is in direct violation of federal law. Federal law is the ultimate authority in the United States of America. They have the right and the jurisdiction to close down these shops. The reality of the situation is that the dispensaries are illegal. They are not in accordance with Federal law.
If the federal government starts closing medical marijuana dispensaries, they will be in conflict with state jurisdictions that approved such medical remedies. State agencies should be charged with closing dispensaries if anything illegal happens such as selling marijuana to those without a prescription. The 10th Amendment to the U.S. Constitution comes into play as any powers not specifically granted to the federal government is given to the states.
The "War on Drugs" is a futile thing anyway. To expand it by going after drug use that has a legitimate medical use-- just because it happens to be the same drug that is illegal elsewhere-- is both a waste of money and an unfair and unnecessary attack on civil liberties.
Federal authorities should not be able to close medial marijuana dispensaries in states in which the citizens voted to approve medical marijuana. Marijuana's health benefits for people afflicted with a variety of ailments has been proven time and time again. There is no point to holding state-wide elections on an issue if the result are not going to be honored by federal authorities.