Separation of church and state in the US is because the founding fathers didn't want a state religion (e.g., like the Anglican Church). But churches in the US are very much involved in government, encouraging their members to support this cause or that, vote this way or that. Whether or not you think that's appropriate depends on your perspective, I suppose.

I like the term disestablishmentarian. And I agree about the charitable component. There are religious organizations that do a lot of good, but there are also good secular ones as well.

Both my husband and I registered with no religion. We got a weird look, and I've had Jehovah's witnesses or something visit me twice, but no problems otherwise.