I have felt the same way when it came to selling vs. holding. I never understood why someone would hold and take a big loss in a bear market for instance, just to avoid paying taxes on a gain.
But larger investors look at risk / reward and when capital gains are raised, the upside potential gets smaller, and they are more apt to pass on some of those investments that they may have made if cap gains were lower. Not all, of course. But it's similar to interest rates with real estate deals. At some point the rates make it less attractive of a risk / reward investment. I'm working on a deal right now where the potential buyer said the lease must return X% above costs on their downpayment to be worth their while. X% - 1 and they are not interested and will look for the next opportunity.
Yes, there certainly is risk/reward factor. Obviously we don't know what might influence the psychology of all traders but I hesitate to fully embrace the provided argument because the capital gains tax is applied universally to all capital gains. I guess more people could stay in cash, but it seems the investors role is to do just that, invest. As you said, if your deal doesn't work the buyer will look for the next opportunity. The real estate scenario laid out is dependent on the investor finding or waiting on a better deal for a variable value item. This real estate investor needs to meet risk/reward criteria that are affected by multiple moving parts (lease cost, rate, down payment, local market....) Always there will be investment options but when the capital gains tax applies universally an investor meets with the tax no matter the investment vehicle.
In any case it does seem logical that reduced capital gains taxes would have an effect on overall market volatility...which would certainly have implications for trading strategies.
As for the Santa Rally...bring it on. I'm ready!