The corollary to who actually benefits from bug reports
The corollary of who actually benefits from bug reports and yesterday's principle is that the more work you make people go through to report bugs, the less bug reports you get, and almost certainly the less good, detailed bug reports you get (because those are a lot of work).
Here, 'work' includes all of the various bits of overhead that you make people go through to file bug reports, including creating accounts. Also, every question that you ask in the process of submitting the bug report is more work, because it is more for the user to think about, especially when they may have no real idea what the answer should be.
The more work you make people do to submit bug reports, the more you will mostly get bug reports from three sorts of people: newbies, the rare selfless volunteer, and people who are nursing their pet cause. Apart from the selfless volunteers, none of these people are likely to give you very good bug reports; the newbies usually don't know enough, and the people with pet causes are obsessively focused.
One immediate conclusion is that Bugzilla is a horrible bug reporting system, no matter how popular it is. Not only do you have to register, but the typical Bugzilla configuration asks you a huge pile of questions, many of which require specialized knowledge to answer correctly.