All these were also examples of mass formation, and in these examples humanity used that power of the agreement of the crowd to better the human condition in substantive and enduring ways.

That's correct, and perhaps it was worth mentioning that, throughout history there were examples of when the free floating anxiety was connected to an object of anxiety, which led people to form masses. In my opinion the issue here is that it's not a conscious process and the willingness to sacrifice for a greater good doesn't necessarily spark from wanting to make the world a better place, but rather from fear and the need to ease in of the psychological pain the individuals are experiencing. Also in the process of mass formation , there's no space for an open debate, as the proposed solutions seem to be presented as the only choice there is. I think, that's what makes it evil in a way.

Matthias fails to note that mass formation in humanity can be a force for good, for forward progress, the evolution of society, and the advancement of civilization.

I'd say that the phenomena itself cannot be said to be good or evil, as it's an undergoing process, or a principle at work if you want, and rather it's application, can be classified, through morality, to be on the one side or the other. Needless to say, the more aware we are of it, the more likely we are to make a conscious decision in regard to it and the more we see that the system itself reaps the power from the individuals, because they shifted the responsibility for their own lives to someone else and allowed them to make choices in their behalf.