I have come to the conclusion that people don't want to make decisions, they just want to be told what to do.
I am a leader of a student activist club on my college campus, and have found that people will help out as long as they are told firmly what to do. So they really don't want to make decisions and come up with ideas on their own, but at the same time they feel disappointed if they are not included in the brainstorming process. The solution: have a list of ideas they can choose from, say what your favorites are and why, and they will usually lean towards what you want to do. So you can do what you want to, and the members feel like they were involved. And sometimes you will get a good group that will actually give good ideas! It always makes me happy to get input from others, because I do not know everything, and I love to learn new ways to improve.
If you are having trouble getting people to step up to the plate, then TELL them what to do. Say you are going to head this section of the event (advertising, fundraising, etc), and tell them what you expect of them. You will need to keep a close eye on them, but it will take a little weight off your shoulders. It's hard to be a leader, especially one dealing with social rights issues, because we all try to do as much as possible to save the world.