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I see dozens of games get absolutely impaled publicly by their closed beta testers.
Companies send out beta test invites because they want to more densely populate their server and see which issues will arise (including bugs, crashes, and gameplay experiences). It is also an excuse to allow the desperate fanbase access to the product even before it is finished.
It is possible to do beta testing with an exclusive group of people who are vetted well by the company, who will respect their NDA. Of course, nobody would like that.
From Darkfall to Neverwinter.... people are posting on the forum reasons 'they won't continue participating in beta' because of some aspect of the combat that malfunctions or what not. These people, rather than reporting the negative experience to the company, as the purpose of their beta test, chose to violate any NDA they had, and publicly ostricize the product.
Companies don't just have beta for you to send in crash reports. If you hate the way your archer plays because of some stupid aspect, they want to know about it, you're there to give them your opinion. The public forum is not the place to deliver it however.
Quitting beta because of a glitch or other correctable gameplay problem is as stupid as quitting your job because they make you work and wait until noon to have lunch.
It is my opinion that companies should very carefully choose their Beta testers, and rather than just a check-box agreement to terms and conditions, should make them first watch a video where someone explains to them what Beta is and what their purpose is and that they're here to play as a job, and not as a game.