It’s impossible to go into a subject as broad as “Race In Science Fiction” in any depth in a one-hour slot, and without knowing how well the audience has educated themselves on the topic, the panelists generally just end up summarizing the background reading.
When doing a general panel, you have two basic options, and I've used both of them.
1) Go ahead and do the summary. It's useful to folks who are new to the topic.
2) Poll the audience. You may find that you've got all novices or all experts, especially if it's a smallish crowd. Invite them to pick a subtopic. I have several favorites -- the midnight sex panel, the xenolinguistics panel -- and they're never the same twice.
What makes this worse for panelists is that, as members of underrepresented groups, we’re in high demand for this kind of “diversity homework.” We get scheduled for these panels instead of panels on subjects related to our actual expertise or current projects. While folks with more privilege get scheduled for memorable topics that will help them raise their profile and promote their work, we’re stuck explaining Empathy 101 to folks who could just as easily look it up on Tumblr.
If you don't want to do a panel because you're tired of it or don't feel qualified, then just say "no thank you" when people try to put you on it. You're not obligated to do it. You're doing them a favor.
Conversely, you can use this as a bargaining chip. A con that wants to represent diversity should be encouraged in that. This makes your uncommon trait valuable to them. So use it as a bargaining chip: "Sure, I'll do Women in SF if you also book me for Meet the Pros."
But getting underrepresented people to volunteer when you don’t have many to start with can be tough.
Best hook for fixing this: "You know how it sucks when there's only one woman on a panel? Can you help us find enough female volunteers that we can put them at least in pairs?" Or whatever. Having multiples of any underrepresented group helps cut both tokenism and stereotyping, because then they can explore similarities and differences in perspective, which makes them happier and the panel more exciting.
Another is mentoring, which is easier if you a diverse con comm as recommended. Ask your experienced pros from underrepresented groups if they would like to coach a novice in the field. This is a great way to pass on knowledge, boost diversity, and encourage participation from new people.
A good diversity panel doesn’t try to tackle the entire ‘diversity issue’ in a single hour. Instead, choose a more focused topic that will give panelists a chance to share their perspective and experience while grounding the discussion in something concrete, so it’s accessible to an audience that hasn’t necessarily done all their homework.
Remember that there are many different ways to make a successful panel. There's a spectrum from the more general to the more specific. Some panelists are good in a wide range, others do better toward one end. The extremes are difficult to do well. Most of the best panels fall somewhere in the middle, general enough to appeal to a large audience yet specific enough to guide discussion. And no matter what it says on the program, if you and your audience decide that it's not working for you, then you can just change it. A panel is a discussion, and it should be fun.