I see this repeated a lot and I'm still not entirely clear why people feel this way. Most major markets in the world have futures/borrow mechanisms, and one of the key reasons is that it allows shorting.
Short selling is a critical element to any healthy market, and we've seen time and time again that markets without well functioning short selling are far more vulnerable than those with (i.e. real estate).
For instance, let's presume that crypto takes off, and business start accepting crypto for contractual obligations. If my future costs are in fiat, but future revenues are in crypto, I have a big mismatch with a very risky asset. A futures market (or shorting) allows me to hedge that risk out and protect myself against future volatility. I can lock in my fiat today, to ensure that I can cover my future costs. Without such a mechanism, I might not be able to risk a collapse in crypto markets.
Mature features (like borrows/futures) in crypto markets should aid in adoption.