My husband is a really intelligent guy, but he does come up with bizarre and rather daft ideas sometimes.
When we were designing our bedroom/ensuite, installing ensuite from scratch, he got really taken with having an open-plan bath in the bedroom, and what's more in the bay window (which looks onto the street!), and then, to separate it off from the room, suggested having a mid-height screen built behind it... that would block the light from the windows into the bedroom. 
He really didn't seem to be able to see why any of this was a bad idea! Fortunately by the time this had happened, I'd been married long enough to realise that arguing what a terrible idea it was wouldn't work, so won him round by telling him why a separated bathroom was a good idea instead.
And when we were looking at secondary schools for DD, one nearby one mostly gives places to churchgoers, so he suggested we start attending church... even though our kids are at a Jewish primary school! He did appear to be serious. Fortunately we hated the school when we looked at it anyway in the end.
You have any examples of bizarrely bad ideas otherwise intelligent people around you have had?