Buying low and selling high isn't all that hard in real estate but you have to live somewhere. Buying and selling doesn't matter much. It's the first time buy that's so difficult, and getting more so.
The problem with the 2008-2012 downturn wasn't so much that people were upside down but had adjustable mortgages they couldn't refinance because they were upside down. When the interest rates spiked, they were screwed. Now the interest rates are so low (artificially low, thanks to the FED). The ones who will be burned in the next downturn are those who lent the money.