Ehtyar, what injustices exactly? I'm not aware of them. If you're just now concerned with [online service] email, then you're way late to the game. How many services have come and gone over the years -- AOL, MSN, Yahoo, MyRealBox, the original Hotmail, etc.?
Google has never correlated user data with user identity, or with the search terms people input. This can be done through cookies and IP addresses. For example, any spam filter has to 'read' the email in order to determine its junk status. And remember, Gmail is more than a mere mail program, it pushes ads and encourages more search (to push more ad revenue). Heck, run the traceroute command at a command prompt on any Linux system (including Mac OS X) or tracert on a Windows system to see the hops that your internet packets go through from your machine to any destination site. Anyone equipped with a packet sniffer at any of those sites can snoop any mail that they want. In fact, the NSA recently proved the effectiveness of this approach by tracking down terrorists by way of their mail traffic.
Privacy is always a slippery slope. But we're already a long way down that slope, and I have a lot more trust in Google to do the right thing to protect my privacy than I have in banking institutions, credit card, and direct marketing companies! (How does every company know that I have a small penis, for example!) The reason I do is because Google could have violated that trust long ago, but hasn't. They still may, but I certainly don't see why Google is being singled out. For me, there are so many bigger issues to worry about, from RFID tagging (see the recent Mythbusters post here on DC) to surveillance cameras on city streets and highways, that programmed scanning of email for targeted ad insertion doesn't seem like too big a deal to me, especially when it's disclosed up front to willing participants in the service.