Activist investors in the 1980s took over a lot of companies and laid people off. I don't think that was necessarily a bad thing, because corporate inefficiency was pretty extreme in that time.

What I think is killing the middle class is upper-class corruption, rampant inequality, generational malfeasance, and political chicanery. "Activist investors" probably don't belong on the top 10.

The argument you would have to make is that the influence of activist investors led to the cutthroat corporate cultures of the 1980s and onward, with "rank-and-yank" becoming normal. But I don't know if that's the case. I will say that the argument can be made.

The argument can also be made that, since what's killing the middle-class is back-scratching, self-dealing, and corruption among a well-connected and entrenched upper class, that investor activism has been fighting against the enemy. I have no idea whether that's true either.