My feeling on it is that these are just the types of limitations you run into when you start using labels to describe large groups of individuals. People have a general notion of what it means to be a feminist, a Christian, or a brony, but it's only a vaguely defined ideal. There's a downside to this, since there are a lot of people who can misconstrue those values or take advantage of them to do bad things. But there's a positive side to it as well, since you get a lot of people coming from a lot of different backgrounds with a lot of different ideas, and there's a certain potential for these people to work together and make use of their individual strengths to accomplish something good.
That said, there's always people who are frustrated by the lack of standards set for joining these groups (especially if it's not anything more than self-selection), and these people do set out to establish a more specific group with more clearly-defined goals. This is why there are different branches of feminist thought, and hundreds of different Christian sects. But these labels come with their own limitations; by setting these new rules, you drastically cut down on the number of people who meet the qualifications for joining, and more limited variety of participants cuts down on the new ideas you can get for strengthening the group. Both of these factors severely limit the power that the group can have for making changes to anything. Furthermore, by establishing and enforcing these rules, you can draw focus away from the actual heart and values of the organization that originally made it meaningful. It's extremely hard to define moral values in such a way that you can enforce specific behaviors to promote only those values, and not accidentally turn focus towards some other, unrelated thing.
In short, groups with vague labels have a lot of power and potential with their numbers, but that power isn't directed very well without clearly defined rules, so you also end up with a lot of bad eggs who misrepresent what's good about the group. Groups with clearer rules are a lot more focused in their power, but they also have a lot less power in general, and