Earlier quoted context omitted.
It's not the morals I'm wondering about; it's the viability of the businesses. Investing in one of these companies is hoping you can cash out before the bubble pops. At least if you invest in a boring SaaS company, when the bubble pops, you might still have a boring SaaS company on the road to profitability.
If an exchange isn't misappropriating customer funds, it doesn't matter if the bubble pops. They facilitate transactions and take a fee in return. As long as they have customers and don't blow money all over the place, they should be profitable.
Even if "exchange" doesn't misappropriating customer funds, the customers themselves can easily become insolvent in a moment, and then it will cascade to every other market participant.