I dont think that mob mentality is always a bad thing. As a species it has behooved us to maintain a certain level of conformity, otherwise the population would disperse or react differently to threats and not remain cohesive enough to survive. And, as contrarians got weeded out of the population, the tendency toward conformity increased.
evolution in complex systems is not this simple. For example the concept of increasing returns dictates that often getting your foot in the door first in a complex environment is more important than being best. Take keyboards - One of the most successful keyboard layouts to have evolved is QWERT, and it was designed to be as slow and inefficient as possible to type on because the keys on early typewriters would jam up if people typed too fast.
I don't think that your argument for how mob mentality could have been an evolutionarily advantageous trait is valid, but, I don't have any argument to present that it isn't or that the opposite is true. Maybe mob mentality is something which is encoded in the genome, hardcoded in the hardware of the brain, or maybe it evolved in human culture, aka the wetware. Or maybe both. Certainly, culture can trump biological traits, in the sense that we may have evolved such that fast food and zero exercise will kill us, yet our culture pushes us towards this lifestyle. Maybe we are genetically averse to mob mentality, but it's our culture that pushes us towards it. All possibilities I think.
obviously mob mentality will continue to bestow evolutionary advantages to many individuals in many cultures for decades if not centuries to come - places like North Korea for example... Consider also that of all 1st world countries, I think it can be said that conformism is disproportionately high in the U.S. It's too simple I think to say that wealth promotes individualism, because hey, the U.S. has hella poverty for bein' a 1st world country. Perhaps even conformism and individualism, when carried to the point of psychosis, are two sides of the same psychosis.
There is a myth of individualism in the U.S., and the U.S. subscribes to this myth. While the U.S. does have a tradition of individualism, and while this tradition did originate in rebelling against conformism imposed by Great Britain, for the following two centuries this tradition of individualism has prospered as a contrast and in response to overwhelming forces of conformism which are domestic in nature and which at present rival, at the very least, in effect and in scope, if not in method, the forces of conformism of Great Britain some two centuries previously.
In the complex environment of culture, advanced such as it has these past few years, I'd say that maybe the only absolute that might be true might be the idea that any absolute is going to be worse than none. And I think that this includes mob mentality.
If I were president, I'd be pushing that fuckin' red button in the briefcase. screw you guys, we're gonna TILT this bitch. We're starting from scratch.