If you want to start a discussion on some WoW forum, you can always complain about the most outrageous requirements you've seen a raid leader set for a pick-up group. And certainly there are a fair number of organizers who set annoyingly high requirements for joining their groups. In particular, many Heroic/Mythic groups will require that you've completed the content before joining their raid.
Many people dislike this and complain that it doesn't make sense. After all, if everyone operated this way, nobody would ever be able to complete a Heroic raid. And this is true. It is certainly true that if the purpose of organizing these groups was to help the general raiding population progress through Heroic content, this would be a very poor way of doing so.
Of course, this is not at all why these groups exist. Raid leaders don't organize raids to help you out, just like you don't join them to help out the raid leader. They organize them because they would like to clear Highmaul tonight, and as quickly and easily as possible. In that light, it makes perfect sense to set the requirements as high as you can while still filling the raid. The fact that it causes an issue for the people they deny isn't even a consideration.
And really, this is the way it should be. But it seems like a lot of people have real issues with the idea that other people are not always required to do things for your benefit.
For example, almost everyone is violently against so-called "day-one DLC" - content which could be shipped with a game, but which the publisher sells separately - even though every argument against it just boils down to "I don't want to pay more money". I agree that if I buy a game, I would prefer it to be as cheap as possible, but that doesn't mean that the game company is required to comply with my wishes.