Antifa isn't a group or organization that holds rallies, and black bloc isn't a group at all (it's a tactic). Antifa shows up when right wing violence is expected. It is a direct response to white supremacist violence; remove white supremacist violence from the world, and you remove antifa from the world. They cease to show up, or show up in a different capacity, usually as peaceful protestors.
Antifa is a desperate last line of defense against white supremacist violence, and not an organization (or, organizations since it is very loosely affiliated bunch of groups with often wildly different ideas about tactics and practices) that seeks violence.
To compare Neo-Nazis to antifa is an irresponsible false equivalence. You can criticize antifa tactics (and, reasonably so, in many cases) without misleading people. There's enough misinformation coming from Fox News and Breitbart about what antifa is and does and why.