It is sad you haven't researched these things for yourself or you may find them equally disturbing instead of dismissing the poor guy as some kind of crazy.
The real absurd conspiracy theories are the one's put out by main stream politicians and main stream media. When the facts are looked into a disturbing truth emerges.
People were once burned at the stake for arguing that the world is round. Others were murdered and tortured for holding contrary beliefs to the catholic church. People like you are the sort of people who were responsible for this irrational purging of contrary ideas because you are incapable of thinking freely yourself.
It is not your fault, you have been conditioned like an animal through years of repetitive dogma that is drizzled onto you by your TV and main stream news.
The utter nonsense that is fed through the idiot box about economics, politics and so on is so ludicrous that when you actually investigate the facts and the science properly and not dismissively you will find that the real crazy people are the zombies who watch TV, drink beer, and "shop till they drop", while millions of people in other parts of the world are being slaughtered with absolutely no justification - and this is being funded by their tax money.
The fact is your husband is going through what a lot of people have been and will be going through in the future. He's an intelligent guy and is clearly searching for a little more meaning and humanity in a shallow and materialistic society that ignorantly turns a blind eye to utter evil. You clearly lack the same insight that he has.
My sympathies are with him.
If you want to strengthen your relationship I would suggest researching these things yourself. The whole area is littered with the most horrific truths it would upset anybody. Typically there is a lot of disinformation surrounding these areas too. You could analyse things together, gather the good arguments and cut away the chaff. Campaign against illegal wars, write to your MP and ask why illegal loans were made to private business using British taxpayers money - a known and admitted 'conspiracy' (look the word up it means something real!)
Your husband is clinging to cannabis to ease the trauma he is going through due to being an intelligent human being with a soul living in a world surrounded by evil and mindless idiots...its not easy. Perhaps if he had someone to share his experience with he wouldn't need to cling to this drug, because in the long run overuse of it will damage his ability to think and behave rationally.
There is some exceptional journalism and science that has been prepared on many fronts. If you want a good introduction into gaining some insight into the real world and not the imaginary one you live in try starting with "Hidden Agendas" by John Pilger. His books have more journalistic merit in one page than most comic newspapers have in their lifetimes. He also quotes all his sources as indeed many alternative media journalists do for people who actually want to scrutinize what is being said from an analytic viewpoint and not a knee jerk irrational opinion which is the way most people operate. Oddly main stream media rarely provides journalistic merit to this degree - and people never seem to question what they are told.
Other books I would suggest for starting out are:
"The New Pearl Harbour" - Michael Meacher
"Confessions of an Economic Hit Man" - John Perkins
Conspiracy theories aren't something to 'be in to' like a mindless fashion trend, a football club, or a fad diet. They are quests for the real truth behind events fed by a natural humanitarian impulse for justice, something the psychopaths leading the herd don't have.
The simple fact is that when you understand the people with all the power are not egalitarian humanists but selfish power hungry mafia types then everything else makes complete sense – the lies about WMD, the Iraq war, 911, the Afghan farce, the banking collapse paid for by tax payers and so on. Of course they'd love people who have realized this to then go on and believe some absurd idea about aliens or reptiles or some other nonsense because it takes away the obvious and striking truth - they are not, they are human (although with vicious psychopathic tendencies) - and if enough people realize this they can be dealt with very easily indeed.
That is why they need to cling to violence, misinformation and their duplicitous charade in order to maintain their positions of power and wealth and they rely on a shallow sheep like herd who cannot mentally tear themselves away from the ideas planted and reinforced daily by main stream media.