Think about how inhospitable Antarctica is. If it didn't have breathable air, it would be like living on Mars. No one has ever lived there as far as we can tell, prior to scientific outposts established in the last 100 years or so. That's been true for millions of years and it will unquestionably be true for 10,000 more... unless of course we manage to melt all the ice by continuing to burn fossil fuels.

Again, the concern isn't about people who might build settlements to drill for oil or extract other resources. People who are doing that will be able to understand warning signs and keep themselves safe, and possibly even recycle what we've left behind. The problem is that, if our civilization falls for whatever reason, people who stumble across our disposal sites might not understand the warnings at all. Or worse, like you suggest, they might treat them like the Pyramids and try to plunder them without the slightest understanding of what they're getting into.

This will not happen in Antarctica because stupid people (as you put it) can't go there in the first place.