When was the last time you went to a decent-sized comic or science fiction convention and didn't see a squad of Stormtroopers? Those guys seem to be as ever-present at cons as they are in the movies! Frequently, the folks who show up in movie-quality-looking Stormtrooper uniforms are part of the 501st Legion, a Star Wars fan club organized around cosplaying as members of The Empire from George Lucas' universe. Calling them a "fan club" is something of a disservice, though, as there are nearly 11,000 active members.
The primary goal of the 501st is "to promote interest in Star Wars through the building and wearing of quality costumes" according to their charter. Though it's hard to imagine Star Wars needing any additional promotion these days, they have additional secondary goals. We'll get to the third goal in a bit, but their second goal is "to facilitate the use of these costumes for Star Wars-related events..." Cosplayers always stand out at cons, particularly when you have a number of them acting as a group, so it's easy to see how going to conventions works in favor of these two goals.
One of the main reasons fans get together is to connect with other like-minded people. The folks who enjoy Star Wars tend to have similar preferences and similar ways of looking at the world, so they get along pretty well. Star Wars acts as a conduit for these fans to form emotional bonds with others who share their ideals. They become friends. Star Wars is a large and diverse enough property that a lot of people are fans, so there are sub-groups that form within the broader Star Wars fandom. Fans of the original trilogy only, fans of the Expanded Universe material, fans of the video games, fans who only collect the action figures, fans who do cosplay... So seeing other fans who obviously appreciate the same aspects of Star Wars that another fan does could easily encourage them to join the group. Which gets to those first two goals they have.
But let's go back to their charter and pick up on that third goal... "to facilitate... contributions to the local community through costumed charity and volunteer work." Their charity page continues the thought: "The 501st is always looking for opportunities to brighten the lives of the less fortunate and to bring awareness to positive causes on both a local and global scale." They've done charity work for groups as diverse as the American Cancer Society, the Make-a-Wish Foundation, the Red Cross, and the Salvation Army to name a very few.
And they're not the only fan group that does work like that. There are sizeable efforts among other fandoms: Harry Potter, Avatar, Firefly, Pirates of the Carribean... It seems as if almost every fandom of reasonable size and organization has turned at least some of its attention to charity work.
There are likely a few reasons for this. From a practical standpoint, these groups can only do so much as strictly a fan group before they start running afoul of intellectual property lawyers. While they technically still violate the law in some cases, it's hard to convincingly argue that utilizing Star Wars imagery without express written permission is more important than raising money for autism research.
But more significnatly, many fans look to these stories for hope and inspiration. Even the guys wearing Stormtrooper uniforms appreciate the good conquers evil message from the Star Wars movies. If they are indeed trying using these stories as aspirational in any way, then doing work for charities that benefit mankind is a key way they can, individually, contribute. They're able to use what makes them happy to help make others happy. And by diversifying with so many charities, all of the individual members can take extra pride in the ones that speak most personally to them.
The Harry Potter Alliance has gone one step further and established the Imagine Better Project. They took their learnings from the charity work they did as the Harry Potter Project and are reaching out to other fandoms like Glee and Doctor Who to help them to help others. They start by asking fans point-blank: "What stories excite you? What parallels do you see between your favorites and our world? How can we use those parallels to realize our capacity to change the world?"
How can we change the world? It's a really powerful question, and one that, until recently, relatively few people have thought to ask. But fandoms are beginning to understand the power behind their communities and organizing in a way that builds that power. And while they may not be building X-Wings and Cloud Cities, they're certainly pushing for the ideals of the good guys from their favorite stories.