Exactly -- reducing the barriers to market entry while increasing widespread market understanding reduces the _unique_ opportunity for arbitrage that Wall Street has enjoyed.

Are we totally sure there isn't an element of astroturfing?

Short sellers participate in this all the time.

Indeed. Hedge funds by nature skim from volatility. When they hold short positions they have "partners" that short and distort.

Everything is astroturfing/selling pretty much nowadays.

Social media is not reality, though astroturfing/distorting can become reality for better or for worse, depends on your position/tribe. What is on the surface is rarely what is the driving force underneath.