There is a reason why we had strict regulations (a dirty word on HN, I know) for "old fashioned" mail and telephone. To eavesdrop on people's private communication was considered a disgusting practice that belonged in totalitarian regimes, and an unacceptable violation of people's rights.
Modern online services have circumvented such regulations, but that doesn't make what Microsoft, or Facebook, or Google are doing any more ethical or socially desirable.
All of this casual disregard for basic ethics can't continue without a serious backlash. And such a backlash won't just hit Microsoft e.a., but our entire industry.
It's time we stopped considering ourselves to be untouchable just because the law hasn't caught up yet, or because the majority of the people haven't figured out what the fuck we're doing.
Some changes through technology are unstoppable. This however, isn't one of them. It's a choice.