You are not bothered that they mine your behavior to better sell your eyeballs to advertisers.
One problem, however, is that governments around the world are using these private corporations as a vast multiplier of state power. The big email providers won’t disclose how many requests for data they get from the government.
Yahoo, for example, has said in court that they should not be forced to release this information because it would be too shocking for their customers .
That sounds bad. But it gets much worse. The Wall Street Journal, among others, has reported on how the US government uses email traffic to build a map of the relationship between everyone in the country:
“According to current and former intelligence officials, the [NSA] now monitors huge volumes of records of domestic emails… [the telecoms] are giving the government unlimited access to a copy of the flow of [internet] communications.” 
The good news is that there are easy things you can do to prevent corporate and state surveillance. The most important step is to use a secure email provider. For more information, see the home page of aktivix
 Gorman, Siobhan. 2008. “NSA’s Domestic Spying Grows As Agency
Sweeps Up Data: Terror Fight Blurs Line Over Domain; Tracking Email.” Wall Street Journal. http://online.wsj.com/article/SB120511973377523845.html (depending on where you are, the url might not work, but there are many mirrors of the article)
Extracted and updated from one of the regular newsletters that riseup sends to its users.