While true, in the US, they're the least bad option - you get them or the Republicans, unfortunately. If the fascists aren't kept out of power, you'll have an active slide toward democracy being dismantled and a series of genocides rather than stagnation and any hope of progress toward a leftist utopia. I really hate to say it, but vote blue, no matter who.

That said, unions and union-adjustment groups are a good start for leftist (i.e. non-tankie) groups - they tend to be practical, and the idea of worker enfranchisement rather than autocracy tends to scare tankies away.