So here is my take on this. I think looking at the Antifa/SJW/Resistance/Whatever else as a monolith is what is the most dangerous. By this I mean they're not all the same. Resistance members are obviously different from violent Antifa and SJW Bronies, but even within the Antifa movement, there are card-carrying pacifists who would do no harm. There are Anarcho Communists and Anarcho Capitalists, all with varying predispositions to violence. There are likely Soros-paid ring-leaders, as well as even darker hands in the pot.
Just like the alt-right aren't just Neo-Nazis. There are libertarians and disenfranchised republicans. There are violent white nationalists as well as black intellectuals. These groups can't be defined as monolithic, or we miss out on a lot of intriguing details. Groups will always be defined by their "loudest" members, but we have to fight that idea.
you are right groups are rarely monolithic. And in our day and age many groups are infiltrated by intelligence agencies or Soros financed people. It's hard to avoid that. The only thing you can do as a peace activist is to stick to the principles you believe in and not blindly follow any leader.
That's the thing, if groups are organized based upon being a group of people, it will fail. Groups have to be organized based upon certain principles, and all members have to hold each other accountable for those.