I was really on the fence with this wanting to believe that his associations were just his naivete or maybe his business dealings, but a reasonable, critical-thinking activist would have seen Les and Tarpley's actions and would not stick up for them at this point.
Big tent only functions by having members of an activist group who actively encourage and promote the Big Tent. I have observed (in general) there is the phenomenon of the "sane moderate": someone who appears to be reasonable on the surface and yet encourages and promotes activists that are disruptive and material that is discrediting.
Put another way: if everyone was reasonable and rejected nonsense, the big tent would not exist at all. It is only because there are activists (in a position of "leadership") who "steer" the movement into associating with disruptors and discrediting the 9/11 truth movement that the Big Tent is effective.
All of this can be observed without determining intent. However, from what I have seen from Sander, he openly associates with someone like Jim Fetzer. This returns us to the concept of the "sane moderate". Regardless of intent or simply bad judgement, the sane moderate regularly apologizes for and associates with obvious disruptors.
The sane moderate apologizes for the disruption and discrediting material or re-frames attacks in an unfair and misleading way. For example, one prominent activist described Tarpleys' slander against Cosmos as a "rift" or "infighting". In other words, reporting attacks is now considered the equivalent of calling someone a Chechen terrorist.