I have no problem with the mock turtle necks. I personally like that the dress of oneself reflects the respect shown for where you are. I like hats forward, no hats indoors, shirts tucked in (although when I was heavier I had a hard time), using the locker room to change shoes, etc.
I am saddened when I go to church nowadays and see people in t shirts or flip flops. I think you dress appropriately for where you are and church was and IMO still should be one of those places. It used to be called "your Sunday's best" as in your nice formal dress. I guess in today's world they are just happy to have people going to church. If you go to church in Europe/UK they dress much more formal and I appreciate that.
Private clubs or higher end publics having a dress code is a safeguard against falling into the guy who is the least common denominator and trashes the traditional dress code guidelines. If you don't have a policy it will denigrate rapidly and respect for the game has then been tank tops and whatever the golfer wants it to be. There is a place for that and it is at a public course with no dress code.
If you go to a funeral you can tell those who are close to the deceased by how they dress, which is more formal. While great that they came, in my experience those not as close will be dress less formally in jeans and a collared shirt perhaps. Just a phenomenon I have noticed and not passing judgment, but the more respect you have for a place the more formally you respect it.
Whether this fits with millennial I don't know and maybe doubt, however shouldn't they be taught some norms of some respected entities and asked to conform as opposed to the other way around?