I get it that people who are trial for a guild want to have a shot at loot. But a lot of trials are also understandable about the fact that they can't get a shot of loot. You have to prove that you are trustworthy person who can pull their weight and where items are not getting wasted on (which are important to actually progress on a group).
Do you know how frustrating it is when you gear a person and that person is joining another guild/quitting WoW during progression because they are either unloyal (guild hopping helps often), or make up their mind about WoW at all and quit? It's a huge hit on the motivation of people building up a raid/guild who put a lot of work into making a guild thrive. I can guarantee that this change will hit a lot of new guilds who try to build up a good raiding guild, because people will get unmotivated fast.
Also the point is that you can always search another raid/guild which do not have such restrictions. That's why people are pissed off. You take them the opportunity to buld their guild/raid as they want it.