I doubt that it is fair to assert that people are acting in a herd mentality merely because TA attempts to both describe and to predict their behavior in terms of what the masses of people are doing or likely to do. 

There is still individual deviation within the pattern that is attempted to be captured by TA, even if the TA has some predictive value and sometimes even very accurate predictive value for the masses, but not necessarily for the individual and does not necessarily take away the free will from the individual, even if the TA might suggest that the individual is engaging in dumbass behavior (or at least NOT as prosperous of a route) if s/he attempts to deviate from what the TA suggests.. which might also pay off from time to time, too.

There are also forces, including individual action(s) that will try with a lot of might to can fuck up the TA, and sometimes will be successful, and surely any TA that is worth any kind of salt will attempt to predict and prepare for deviations and destruction attempts, too.  Successfully?  Perhaps sometimes.  Surely some models are better than others and sometimes some models have to be thrown in the rubbish and some models merely can be tweaked in order to make better at both description and prediction.