"The liberation of the human mind has never been furthered by such learned dunderheads; it has been furthered by gay fellows who heaved dead cats into sanctuaries and then went roistering down the highways of the world, proving to all men that doubt, after all, was safe — that the god in the sanctuary was finite in his power, and hence a fraud. One horse-laugh is worth ten thousand syllogisms. It is not only more effective; it is also vastly more intelligent."

Prejudices, Fourth Series (1924)

I know I'm in a bubble when I start rejecting some facts because they conflict with what I'm already presuming.

Loads of apologists love to tell us atheists that everyone has faith, even us. (Obviously, this is true, but that doesn't give faith any epistemic validity.) We can still be humble and admit this, but at the same time proud of the fact that we're atheists and have planted our feet outside of what we identify as the wrong bubble.

Here's an example I like: Take your average layperson who believes that matter is made of atoms, or that biological life is made of cells, and ask that person, "Where's the evidence for that?" Most people don't know the evidential basis for even the most basic scientific ideas, and yet they believe them. This is somewhat appropriate, because not everyone can be experts in all of the world's history and the sciences. However, such beliefs should be held provisionally and uncertainly. Furthermore, it is inappropriate to claim such beliefs with an air of authority and knowledge when you do not have those things.

Freethinking is a continuum. There are those who break free of the religious bubble but are still stuck in some larger bubble. In fact, I sometimes think that I will forever be pinpricking my way out of bubbles for the rest of my life. I may even inadvertantly step into other bubbles.

I know mike above already said it, but this strikes me as particularly perspicacious, too. It ought to be enough to keep us somewhat humble so we never claim we've "arrived." All of us are laboring under some misapprehensions, some way in which we're not perceiving reality clearly. We've got to keep on keeping on bursting bubbles--often our own.

There are those who break free of the religious bubble but are still stuck in some larger bubble. In fact, I sometimes think that I will forever be pinpricking my way out of bubbles for the rest of my life. I may even inadvertantly step into other bubbles.

I really like that metaphor, Polly.. I think it's easy to fall into the trap of saying: just because I'm now an atheist, I'm free of delusion. Losing religion shouldn't be the end, but the beginning of the journey.

I know I'm in a bubble when I start rejecting some facts because they conflict with what I'm already presuming.

Freedom is relative and not all atheists are freethinkers. Some just don't believe in god but not because they're skeptical or inquisitive in general. Some xians can be more free in their thinking than some atheists who are tethered to non-religious dogmas.
It's all about shedding one's presuppositions, whatever they may be. And it's a monumental task. I really do credit the INTERNET. Not just information, but discussion and the availability of real life people holding really different POV. It's a godsend...hehehehe

That's all it really takes to destroy their bubble...

I would phrase the metaphor a little bit differently: that's all it takes for them to see their bubble. Once they see distinctions between inside and outside the lens, religiously-raised believers will be able question the arbitrary reasons that they're in the bubble to begin with. (Community, tradition, faith, family/friends, feelings, social pressure, positive social activity, etc.) Obviously, some believers will keep to their bubble and try to defend it. Hopefully, though, they'll decide to work their way out and start thinking about things "in the clear air" before confining themselves inside the bubbles they were put in.

"As long as the internet is open and supplies contact with various thoughts, it doesn't matter what's true/false information. Atheism should follow from free-thinking, and so freethought should be the primary concern if we want to eventually promote atheism in an honest way."

And that's the whole point: so long as there are opinions that contradict those put out by the leaders of society and religion there's no way they can ever re-establish their monopoly on information! It doesn't matter how much "truth" there is in the conflicting information - all that matters is that there is conflicting information that can be easily accessed. That's all it really takes to destroy their bubble...