I doubt that anyone is claiming the right to define what is worth complaining about. The issue arises when people start forcing the issue across multiple threads, including threads that have nothing to do with the issue at hand. To give you a recent example: people did not like the inclusion of the page header/title bar in 2.5.2. There was nothing wrong with disliking the change. There was nothing wrong with bringing it up. There was nothing wrong with devoting treads to it. Then someone brought up another thread to discuss the bugs and features of 2.5.2, and explicitly asked that the title bar issue not be brought up. The reason was clear: there were already several threads dedicated to the issue, and certain members of the forum wanted to be able to discuss other aspects of the firmware revision without sorting through a singular complaint that was very well known.

Things like this have also popped up in the past, to a greater or lesser degree. Some are pure design considerations which certain people didn't like and other people did like, such as the carousel in the 1.9.x firmware. Others were bugs that clearly needed to be addressed. Example: certain members didn't seem to realize that it affected some users but not others, and that the ones who didn't encounter the bug didn't want to be stumbling across it in virtually every thread.

I think it's safe to say that all Kobo lovers realize that. I think that it's safe to say that all Kobo lovers are okay with listening to the issues that other people have with Kobo devices, and acknowledge that those issues are real. (In some cases, they may not agree with the criticism but they acknowledge that people's tastes differ.) I'm not sure that Kobo haters realize that some people love their Kobo or, if they do realize it, they are being incredibly disrespectful about the interests of those other people.

One again, there is nothing wrong with bringing up an issue in a general thread. There is nothing wrong with having a thread dedicated to an issue, or several threads for that matter. There is nothing wrong with voicing support for Kobo resolving an issue. There is something wrong when the lobbying effort starts to demonstrate disrespect for those who disagree with something being an issue. There is something incredibly wrong when disrespect is being displayed to people who agree that something is an issue, but wants to discuss other stuff.