[learc83]

>I'd guess about half of that identify as Christian because it's socially unacceptable to be agnostic.

That's much less an issue now than 50 years ago though, which is what's important when talking about a relative decline. It was much less socially acceptable to identify as agnostic in 1960 than it is today.

[WalterSear]

Still a huge issue in much of the US.