I still don't see what keeps you or any of the numerous people who have an issue with that from starting your own raids without item reservation then. As I already said, this is exactly like ganking. It's certainly not fun for the people getting ganked, but it's part of the game. People have to find their own way to handle it.
The loot doesn't belongs to the group. It belongs however the loot rules are defined at the beginning. That's why there are loot rules stated before a raid even starts. You join one fully aware how it will be distributed, including items the leader is reserving. What do you do when you don't agree with the loot rules, even when there aren't item reservations? Normally people just don't join something they don't agree with. People organizing something aren't forced to accept your terms, it works the other way around. Otherwise what would be next, people would want Staff to forcibly include someone in some top guild because they want in, but have been rejected... and you know how hard it is to join a top guild when you don't meet their requirements or disagree with their rules.
You can't depend on Staff to intervene with something that isn't against any rule or game mechanics, simply because you consider it unfair or dislike it. Fixing this "problem" might be up to the people who consider it a problem working together.