I think we can probably just state the rule as follows: Dress in a manner that is appropriate for the environment. If a church's congregation has decided to go casual, so be it. If they're dressier, you should do the same. If you're going to the opera, dress more formally, if you're going to a dive bar, leave the tux at home.
I still have a problem with costumery though. And that's pretty much what I think of ties. At least I can see some sort of semi-function for a sport coat.