I'm not sure how the BLM organization is dangerous, and if an organization "whose mission is to eradicate white supremacy and build local power to intervene in violence inflicted on Black communities by the state and vigilantes" is divisive, surely it's between those who are in favor of white supremacy and those against?
The biggest criticism I've seen of BLM (organization) is that (some of?) the founders are allegedly Marxists? If true, I don't see that as particularly interesting thing in and of itself. What is this, the 1950s?
ActBlue (the payment processor you mention) is a non-profit, not owned by the DNC, see wikipedia/actblue.
If you think I missed something important and want to have a good-faith(!) discussion about it in the comments, I would be happy to. Otherwise --perhaps it would be worth re-evaluating and re-fact-checking the concerns you have about it?