You're trading security for anonymity. That's should be Tor's unofficial tag-line.
I don't even need to convince you of Tor's relative insecurity, there is a front page article right now all about it:
The major users of Tor need to consider even their ISPs as an adversarial agent - that they are being actively monitored and MITMed. In this sense, these users are not trading security for anonymity.
For those who trust their telecommunications carriers (in the US even in the face of CALEA) - they are certainly introducing a MITM. It's also important to note that the linked article considers the 'security bug' to be owned by software updaters and software vendors that that do not sign binaries - the vulnerabilities are not specific to Tor, but it does provide one mechanism to exploit them.
This is all a good reminder, as the Tor team themselves regularly say, that secure operational browsing and software practices are crucial to anonymity and security even with Tor installed.
From that article... "anyone with $3,000 could de-anonymise users of Tor".
That article was from July 2014. As far as I know the fix isn't implemented yet, but I could be wrong. Here's the most recent article I could find about a fix... http://securityaffairs.co/wordpress/26982/hacking/tor-workin...
Remember the "Tor Stinks" slide from the Snowden leaks? The NSA, with direct taps on the internet backbone, has had lots of trouble deanonymizing Tor users.
Everyone's data gets sucked up as the default, but with Tor - I think they Snowden docs showed they could only get about 1/4 with automation. I do not remember the exact percentage.
The combination of CALEA, Stored Communications Act, and Patriot Act under the Third Party Doctrine mean the system stores and processes our data by default, over a sliding window. (IIRC there were some Snowden programs that had windows of around 5 years?)
With Tor you increase the cost to taxpayers a little and decrease the chances (especially with good cyber hygiene) that you'll give everything. If you use a cell phone you give your exact time and place 24/7. Even local police have access to these cell phone tracking databases. You can't Tor a cell phone.
Tor isn't really a good answer to the system. But if you need privacy, there's a corner in Tor.