After recent (and in some cases very dramatic) bearish conversions by the likes of JPM, BofA (BAC), Citi (C) and UBS, the only bank that steadfastly held a bullish view on stocks during the recent market squeeze higher was Goldman Sachs (GS).

Not any more.

On Thursday, Goldman strategist David Kostin appeared on CNBC, where he too joined the bearish crowd and said that based on the threat of margin collapse ("35 out of 53 tech companies had margin declines") and record-high stock valuations this year, it's time to play defense in "a tough market."

He also hinted that with 80% of fund managers underperforming their benchmark, the probability of irrational capital allocations increases, and as a result there is a "reasonably high probability" of a large drop (or "drawdown" as a sudden plunge is called in polite circles) in the S&P 500 ahead of his year-end 2100 price target.

Then overnight, Kostin dedicated his entire weekly kick start piece to just the topic of a drawdowns, saying that "Unbalanced distribution of upside/downside risks suggests “sell in May” or buy protection." He adds that "we continue to expect S&P 500 will end 2016 at 2100, roughly 3% above the current level. However, a shift in investor perception of various risks could easily trigger a drawdown."

Goldman's stark and unexpected warning is driven by risks which include "elevated valuation, investor positioning, money flow trends, uncertain interest rate policy, weak economic growth, and election year politics. A 5%-10% drawdown in S&P 500 during the next few months implies an index level of 1850 to 1950 and a forward P/E of 15x-16x based on bottom-up consensus EPS."

Of course, a 10% market drop never ends on a dime, especially in a market as illiquid as this one, and if the recent warning by JPM's Marko Kolanovic is correct, should stocks stumble by 10% in the absence of another round of central bank intervention, we may be looking at the first official market crash in the post-cri

And just like that Goldman has joined the bearish camp.

To be sure, for Goldman faders and contrarians, this may be the most bullish catalyst yet because after the anti-Dennis Gartman ETF, doing the opposite of what Goldman recommends has historically been the most profitable trade.

Still, perhaps this time Goldman is not seeking to unload its book on muppets. Here is the full reason behind Goldman's bearishness.

So fade Goldman again, or assume that after a series of abysmally incorrect calls in the past year it will finally be right? We let readers decide.