That said, I believe in the Efficient Market Theory, but only over time.
I watch the market all day everyday as I work on other stuff and think the recent gyrations are due mostly to a slowing world economy, China-trade uncertainty, algorithmic trading, and the general uncertainly of Trump's efforts to repair some major imbalances in world trade that have worked to the disadvantage of the U.S.
As an aside, the market volatility is also a consequence of having Trump pull down the curtain that has hidden what China is doing to increase its influence around the world. Along this line, I heard the other day that China was offering free telecommunications infrastructure (ZTE, Huawei, etc.) to developing countries which would give China a huge platform from which to spy on everyone who dealt with said countries. That is part of the reason the CFO of Huawei was taken into custody.
Lotta stuff going on that has come into the public view. I think it a good thing that we know what is going on in the world, but the markets do, of course, factor all that into prices.
If I weren't already all in, I would also buy in right now.
You’ve correctly noted a lot of the “reasons” for a downturn. Others include the fact that indexes are so easily bought, sold, shorted or even “ultra shorted” (2 or 3 times downward movement funds and ETF’s).
The craziest thing about it right now is how Goldilocks everything really is with the US economy. Low unemployment, high corporate profits, less regulation, low inflation, low energy costs, low borrowing costs and to top it off a record holiday buying season.