Lady of the lake
You mean like when I became an atheist and didn't tell my extremely fundamentalist christian family about it? It was none of their business, so I didn't start nothing, and there was nothing. Although eventually (years later) I got pissed about having to deal with my family's christian sensibilities every day so I laid into them about their hocus-pocus and they reacted as you can imagine. There was much wailing and gnashing of teeth on their part, I cared less than a nihilist with a marmot, and life went on as usual. They still haven't gotten over it, and I still have yet to give a damn about their opinion. It ain't a big deal.
You can't compare that to coming out as gay.
Fundies can start to accept a gay son or daughter sooner or later because hey, you are still their son/daughter! They loved you before you came out and sooner or later they realize that nothing has really changed and that it doesn't matter.
But "coming out" as an atheist and flat out telling them that what they believe is nonsense? Oh boy. These people are brainwashed. They can tolerate other people but if you start to criticise their beliefsystem itself they get really pissed. Because in that case you have actually given them a "proper" reason to be pissed off. You didn't make it about you and who you are, but rather about them and why they are loonies.
Sure, there are some people who are so far gone they even throw you out just for masturbating or having softcore porn on your PC but I would try to get out of a household like that anyway.