Well, not quite a mockery, since they do require a fair bit of evidence to convict, but yes.
The real problem is not the trials but the rest of the process- The Doom is far to harshly restricted and far too rarely leveled.
Honestly...
how do we know that?
We don't have much in the way of information on the recidivism rate of warlocks, what we do have tends toward: they usually repeat offend. Apparently, over the centuries, the Council has tried a lot of different things to try to rehabilitate them, even
Harry admits this, and he also tells Karrin that pretty much none of it ever worked very well.
We know that it's
possible for a warlock to turn away...at least in the early stages, sometimes, with help. We've see it with Molly and possibly with Harry. (We don't technically
know if Harry ever was one, even he isn't sure
exactly what happened in that fight with Justin). It looks as if it happened with Margaret, though we don't know the details and how hard it was for her or how much help she needed.
But note that even in the case of Molly, it was a major struggle, she nearly fell several times, she needed help from Harry, her parents, her siblings, Lea, and to a lesser degree others as well, to get back on track, and it took a
long time. That was after
one significant offense, with semi-good intentions and results that were not 100% bad.
What if she had messed up 3 or 4 times before Harry caught her? What if her initial act had been less mixed, more purely selfish? What if she hadn't had the family she has, the father she has, and a Wizard of the White Council who knew her since she was a kid?
The Doom is harsh, but I don't think we can say with confidence that the Council should allow it more often or less stringently.
(Also, I suspect the Doom is only required for convicted warlocks, I doubt a talent caught in the early stages of the grey areas necessary requires it.)