I like the perspective, but I disagree with your assessment:
In the article Goldman Sachs is stating that cryptocurrencies are worthless
That doesn't appear to be what they're saying. In fact they specifically said that the underlying technology is valuable.
Strongin was more upbeat about the blockchain technology that underlies digital currencies, saying it could help improve financial ledgers.
They did say that most cryptocurrencies could bottom out to zero. This is supported by the data - Every time Bitcoin crashes, every other crypto crashes. If cryptocurrencies were independently valuable, this would not happen, but this shows that their values are not independent. This is not a problem with the technologies themselves. There are a number of different purposes and different technologies behind the various cryptocurrencies, and logically many other coins should be more valuable than Bitcoin.
The issue is that investors are uninformed. There is so much money being blindly thrown around with so little knowledge about the underlying technologies.
We can draw a parallel to the Dot Com bubble. If you had invested in AskJeeves, HotBot and MetaCrawler back in the 90s, you would be sorely disappointed today with your return on investment. Google was not even a player at the time.
I feel like most of today's cryptocurrencies are probably going to be insignificant in the long-term, much like those obsolete search engines. The question is, what coin will become the Google of cryptocurrency?
So far Ethereum looks like the strongest player to me, but that could change very rapidly if new technologies come out that make it obsolete.
The underlying technology blockchain is not cryptocurrency. Blockchain is a method of organization and tracking. Lets say if you want to keep track of all medical records, the technology blockchain can do it. It dosen't have to have a currency to make a blockchain. By stating that blockchain can improve financial ledgers is only stating that they would be interested in changing the way that they keep track of their ledgers. It doesn't mean that they support cryptocurrencies in any way. Most cryptocurrencies use blockchain technology. Cryptocurrency and Blockchain are however not the same thing.
Goldman Sachs telling people that cryptocurrency is bad is like Apple CEO telling people that Samsung products are bad. A better analogy would be like Walmart CEO telling people that buying merchandise with Amazon is just a fad and Amazon will eventually go out of business.
To put into perspective the desperation of Goldman Sachs:
It should be noted that Goldman Sachs does have some stake in crypto - They were the majority stakeholder in Circle back in 2015.
The fact that Goldman Sachs is criticizing crypto is definitely in their business interests, there's no question there. It's a market that they don't have a strong foothold in, while several other major institutions are doing much better. This however does not make their criticism any less valid. Look at the facts in the article, rather than writing it off because of the author.
It's extremely troubling that all of the coins plummet everytime Bitcoin drops in value. This is either an indication of a lack of knowledge on the part of investors, a lack of differentiating features among the products on the market, or a systemic problem with the trading market itself.
So... when the stock market corrected a few days ago and most of the stocks went down loosing 4 trillion worth globally, with that kind of thinking you must believe that investors in the stock market also have a lack of knowledge....
If PetroChina were to lose 50% of its value, the stock market would hurt. There would be cascading effects across the markets and those effects would be fairly drastic. However it would not be realistic to assume that General Electric would also lose 50% of its value because of PetroChina's crash.
If Bitcoin were to lose 50% of its value tomorrow, we could reasonably expect every other cryptocurrency to also drop by an average of 50% (Except for Tether). We would expect this drop in the small altcoins as well as more major altcoins like Cardano and Ethereum, even if the reason for Bitcoin's crash had nothing to do with the other coins that are affected.
The reasons for that are debatable. I'm not saying that everyone has a lack of knowledge, but personally I see enough differentiation between altcoins that a movement in BTC would not cause me to sell my ETH or vice-versa. Maybe that just leaves me as a bag holder ;)