Hacker builds Tor tracking system
thesecuritytimes.com
thesecuritytimes.com
If I have to chose between a police state and paedophiles, I'll take the paedos. At least they don't have guns.
The basic failure is that plenty of people think that by using Tor they are anonymous.
I'd rather have them think that and then have the real perps run in to law enforcement than to have the people that have real secrets to share and are stupid run in to law enforcement.
Any darknet that functions without flaws is enabling criminals as much or more than it enables legal uses, any darknet that is flawed by extension will help to catch a lot of criminals.
When you are doing stuff that can not stand the light of day it is probably best not to use technology that you do not fully understand.
Unfortunately, plenty of "good guys" like whistleblowers and human rights advocates that need anonymity for very good reasons are probably not going to understand the technology behind it very well, with very few exceptions.
Some techies understand it, of course... but probably not "fully", as very very few people are well versed in technology from the lowest hardware level to understanding networking details to being qualified to do crypto algorithm analysis, etc.
At some point, most people just have to trust the technology and what other people they respect tell them about it if they're going to use it at all.
Pointing out failures can, hopefully, allow to build better law-enforcement-evasion tools in the future. As HD Moore also pointed out, any such tool has a social price built into it.
To classify TOR as a law-enforcement-evasion tool is to miss out on a great many legal uses such technology has.
Law enforcement evasion is specifically something you probably should not do with TOR, since you abuse the trust of the exit nodes.
The paedophile example is an extreme one. There are many countries where criticizing the government or reporting on public unrest may land you in prison. While those uses are, essentially, illegal in those countries, I would have little problem aiding people who disagree with laws I find unjust to evade their local law enforcement.
Also, I am pretty sure there can be no such thing as a perfect darknet, but I really don't want to do the math.