Sounds like you have a very oafish brother-in-law. One thing you could have mentioned was Ron Paul's quote "It is no coincidence that the century of total war coincided with the century of central banking." Follow up w/ "if people realized that money printing (a.k.a. 'inflation') were really a hidden tax then the public wouldn't have put up with it for this long." Then mention that the price of gas (and things in general) are rising as a result of these wars. He may not believe you but it's better for him to have at least heard it from you prior to our impending economic crash (so at least maybe he'll pay attention afterward rather than blindly trusting TPTB when they push more government as the solution).
Personally I think it's better to start small and find something that he's upset about (maybe gas prices are a good example) and try to win him over on that argument. Eventually it can lead him all the way down the rabbit hole.
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