Actually, the product is legal in the State of Michigan (and in a number of other states) but illegal under federal law. Local governments, such as this township, base their laws and zoning policies on State Law because it is the State that governs what local governments in their state can and can't do. Federal laws do not regulate local governments. That's why the township's zoning ordinance was re-written specifically to make medical marijuana grow and distribution operations a special use permit in a specific zoned area (in this case, it would be in an area zoned I, which, BTW, doesn't allow for churches or most schools (post secondary and trade schools excepted - and most laws barring operations within a certain feet of schools exempt those type of schools - not even with a special use permit). They've come in to compliance with state law. Just as a local police officer can't enforce federal laws (which is why sheriffs and police chiefs in border towns keep getting their hands slapped by the courts every time they try to enforce federal immigration laws), the local governments can't ignore state law just because it conflicts with federal law.
Right now - the product is a mix of legal and illegal. I know a lot has been made of the President telling Federal Prosecutors not to enforce the law, but if you've paid any attention at all to this administration and how this President thinks (and not just gotten your news from the screaming pundits on your favorite cable news channel, of any political stripe), it's not for partisan political reasons at all but is very consistent with his belief that if a law is outdated and needs to be changed, it should be changed by Congress and not the Courts. It's very much like his stance on the Defense of Marriage Act - activists on both sides were surprised to see that his administration was opposed to trying to get the law nullified in court - instead, he wanted Congress to nullify the law. It's pretty clear to most people that if a federal prosecutor in a state where medical marijuana is legal decides to enforce the federal law, it's going to end up in the Supreme Court where it becomes a State's Rights case and where it is likely that the federal law would be struck down in favor of the states regardless of the flavor of the make-up of the court. That's something this President has a fundamental objection too - he'd much rather that Congress be the ones to change the law - and it's not yet being pushed because there isn't the critical mass of states that have changed their laws yet to make it untenable not to do anything - but there likely will be soon.
Without the publicity this has received, I doubt that anyone would be able to tell up by looking at the building (once it's built) that the building is a grow site. There are now farms being set-up in industrial buildings and no one could tell if you just drove by one.
As for the technicality of it being illegal to be illegal in the US , the MA Attorney General has it exactly right. Under federal law, it is a criminal offense to cross the border without documents, but like many laws of that sort, you have to be caught crossing the border at the time you cross the border. So if you have crossed the border without being caught, you can't be charged later with crossing the border. But your still in the country illegally - however, under federal law, being in the country illegally is not a criminal offense - being in the country illegally is a civil offense.. What is a criminal offense is being in this country illegally if you have already been caught once and deported.
I'm just not that concerned with whether there is a Scout Council office somewhere near a grow operation - perhaps because as a Scout, I knew where the illegal pot patches were located in the farmer's fields next to the local scout camp, where it was in the local scout camp, and where it was at both summer camps I went to/worked at. Of course, this was the 1970's - and although they may not be as well known anymore, or even forgotten, it wouldn't surprise me at all if they still didn't exist in a wild state (hint - look for big areas of ragweed - then look more closely at some of the plants that might be interspersed among them).