Think of it this way: cheese was a normal part of everyday diet for most of the world for centuries before invention of modern refrigeration. It doesn't need to remain at a consistent 33-38F for every moment of it's existence otherwise it will rapidly spoil.
A cheese like brie is actually much better at room temperature than refrigerated–it softens up and will have a much creamier texture as well as more pronounced aroma. In France a lot of families don't even refrigerate their cheese at all, they stick it in paper though, or put it on a plate covered by another plate.
Traditionally it (and most cheeses) would have been kept "cool" in a cellar or cave for storage, somewhere between "room temperature" and modern refrigeration. For serving it is recommended that you actually leave it out on the counter for 30-60 min. or so to come up to room temperature.
Unless you live somewhere tropical with lots of fungus or mold issues, by leaving it out overnight you have only slightly shortened the expected shelf life of a cheese which would normally be perfectly fine for weeks in the refrigerator, especially since it was already sealed in a container that would keep out germs/bacteria anyway. The biggest threat to spoilage of a cheese would be exposure to mold spores through the air, and being in a plastic bag basically means the likelihood of that happening is low.
If it was already contaminated with mold before you put in the bag, then you have only accelerated the process a little by giving it a better climate to grow and it will just get moldy a little bit sooner (maybe a couple days) that it would have it you had not left it out.
I think it is quite strange that people are so paranoid about food spoilage with things like this. Do you know how this stuff is made? How do you think people survived before the 1940s?
also, as a side note I'd recommend storing it in something other than plastic.
It actually benefits the cheese if it can "breathe". Brie typically comes wrapped in some type of parchment paper-type product (or special cheese paper) for this reason and typically that is all you need so it is overkill to then put it inside a plastic bag on top of that. Brie goes bad in two ways. It becomes ammoniated and smells VERY VERY strongly of ammonia. Or it goes moldy.
Yes, it will allow a little moisture to escape and it can get dry over a long period of time, but plastic is worse because it holds in too much moisture (or traps moisture from the atmosphere) and can actually cause it to go bad faster and develop "off" flavor and texture.
Paper is adequate to keep out mold spores and other things that will make you cheese go bad so it isn't necessary to have something airtight or impermeable.