There's nothing anyone can do to possibly stop it. How does one stop money exactly? I feel your sentiment though. When the institutional investors join in and come flooding with cash, the price might start to fluctuate violently. If those same investors where to pull out the same way in which they came pouring in, there would be a massive move on the markets every time. Look back at what happened the other day when the price had sharply fallen, I'm not an expert, but big money does mean bigger trouble in this instance.
I don't agree with your statements. So you are saying that the volatility was lower when the institutional investment was not there. It is simply not true. Back in 2015 and 2016, there were incidents in which the prices fluctuated by as much as 30% or 40% in a single day. Therefore I would argue that the institutions have lowered the volatility levels. BTW, why should long-term investors worry about price volatility? Temporary fluctuations should not impact them.