When Oregon legalized marijuana the price dropped significantly - there were farms/distributors everywhere. Feds are upset because Oregon suddenly became a major distributor of marijuana to other parts of the country where weed was still illegal.
I suspect the Feds will eventually drop there objections to Marijuana - it has become pretty clear to the states the have legalized it that it hasn't ruined society and none of the "sky is falling" predictions have come true. For the most part the police endorse the legalization as it allows them to spend time on serious crime. Anyone who has followed the "war on drugs" knows its an expensive failure.
