That being the unethical brokers that sell investors nothing but worthless fake shares without their knowledge.
How on earth is your brokerage supposed to determine whether shares are worthless, or "fake"? It isn't his business to do your DD for you. You appear to advocate complete irresponsibility on the part of the "investor". You think he should be able to buy very high risk stocks--look at all the complaints from people who've been prevented from buying stocks on brokerages' "Suspicious Activity" lists--and yet if anything goes wrong, the brokerages are responsible.
That's just wrong.
People who bought CMKX and hung onto it did so at their own risk. God knows it wasn't for a lack of warnings.