Great article. Thank you.
You make many good points but I think the extreme left wing group you are pointing to are much smaller than they seem in the media and have almost no power. In fact their almost complete lack of power is the biggest source of their rage.
Even within the Democratic party the group have almost no power. They were completely rejected in the last two nomination fights (and we could argue in the Obama years too) The nomination of Joe Biden with no consessions whatsoever to the the left wing of the party shows no there will be very little change in the coming years if he wins.
I think a better strategy, one you allude to I think, is for the mainstream to make some concrete progress on the social justice issues. The activist base will not be satisfied but the basic left and liberal voter will be supportive of moderate change on those fronts without going into the areas you seem to be afraid of.
I guess we will see in the next 6-8 months.