What you select for when you make something harder
There is a general belief that when you make it harder for people to do something, you will get better results; better bug reports, better blog comments, and so on. This is simplistic and, I am convinced, false in practice.
The basic principle is simple: when you make things harder, you do not select for quality; you select for people who care enough.
(Well, not entirely; you also select for people with lots of spare time and for people who don't realize how much effort they're expending.)
Only sometimes will the people who care enough also be the people who will give you the sort of better results that you want, because there are all sorts of reasons that people wind up caring enough about something. (Conversely, not everyone who will give you quality results will care enough to do the extra work, although this may be considered acceptable.)
This leads to a corollary: if you are stuck with undesirable people, making things harder will not necessarily make them go away. Instead you may refine your crowd of undesirable people down to just the most fanatical (and thus annoying) ones, because those are the ones that care enough to stick around despite the all the annoyance you are putting them through. And in the process you may have lost most everyone else, because as a general rule the fanatics will care more than the regular people and thus the regular people will drop out sooner.
(See, for example, the relentless evolution of CAPTCHAs under the pressure of spammers into completely unreadable things that only spammers will bother to decode.)