Who is still using these sites after all of the Silk Road 1.0 arrests? You have to be pretty dumb to risk your freedom on some stranger's computer security skills.
And not just some single stranger.
How many thousands of programmers/engineers are indirectly involved?
Can you trust the programmer of the website?
Can you trust the programmers that wrote the webserver code?
Can you trust the programmers that wrote your web browser?
Can you trust the programmers that wrote BASH?
Can you trust the programmers that wrote the rest of the OS?
Can you trust the programmers that wrote the BIOS?
Can you trust the engineers that wrote the CPU's microcode?
I once had this wild idea of trying to come up with some automated proof system that would help insure program correctness. I then looked at the huge amount of errata for Intel processors. How can one be sure one's program will even run as expected when the processor itself can't be proven correct?