I don’t think social media is necessarily “broken,” but the efficiency at which it can organize a large number of people is certainly scary. As with anything powerful, it can be used for good or evil.
I don’t see a way to curb this power without imposing deliberate inefficiencies. For instance, if we legally capped the number of users each social network can have, it would curb the “network effect” and promote more competition. Organizing will be more difficult because of the fragmentation.
You might argue that we shouldn’t diminish the effectiveness of good causes, but every good cause is a bad cause to someone else, and vice versa. Unless we live under a dictatorship, there is no way to determine who is good and bad absolutely.
When you fight for a cause, you always have opponents. If social media is powerful for you, it’s equally powerful for your opponents. By making our shared weapons more powerful, we ultimately gain nothing. The question is which we should pick: The possibility to do massive good or to prevent massive evil?