Goldman Sachs is not opening a bitcoin trading operation because they believe in the legitimacy of blockchain tech. The only reason Goldman is doing this is because they smell money and realize that jumping into a bubble can net them hundreds of millions/billions of dollars in profit. They are not going to make money from buying bitcoin, they are going to make money in fees they charge other large clients to buy/sell/hedge/etc bitcoin. They'll also create some exotic bitcoin-based financial instruments that nobody can understand but will sell to pension funds for gobs of money.
Will blockchain revolutionize tech and business in general? Will a Bitcoin be worth a million bucks some day? Will crypto replace traditional currency? I don't know - but I guarantee that is not the angle Goldman is playing here.