Yes, the leftist are "arming up",, just read some of the "Reddit Groups" that cater to Leftist/liberal gun owners.
They are VERY clear and state often that they are NOT "liberals" but are leftists.
They are also clear why they are arming up,, and it is not to protect your constitutional rights. But to inflict their will on all those that oppose their agenda.
I think you are referring to is r/SocialistRA. Socialist Rifle Association. 98k members with a strong facebook, Instagram and Twitter presence along with local chapters and paid membership programs. I think they aim to be the political Far Left equivalent of the NRA.