https://www.finra.org/investors/need-help/your-rights-under-sipc-protection
SIPC provides limited coverage to investors on their brokerage accounts if their brokerage firm becomes insolvent.
Your brokerage is not insolvent.
SIPC does not protect against market risk, which is the risk inherent in a fluctuating market.
Value goes up... value goes down... that's market risk.
Every brokerage website I've ever seen has text like this (which I got from chase.com) somewhere in the fine print:
Investing involves market risk, including possible loss of principal,and there is no guarantee that investment objectives will be achieved. Past performance is not a guarantee of future results. Asset allocation/diversification does not guarantee a profit or protect against loss.
EDIT:
Or all of the stock holdings in the portfolio are safely transfered free "somewhere" for you to continue holding if something like MF Global case happens?
Yes, that's exactly what SIPC is for. If you had 1,000 shares of Chevron at Man Financial before it collapsed, you'll get your 1,000 shares back.
It might take time, though.
https://www.sipc.org/news-and-media/news-releases/20160209
Securities and commodities customers of MF Global Inc. have had all of their assets returned with the conclusion of the MF Global liquidation, the Securities Investor Protection Corporation (SIPC) announced today.
“After more than four years of recovery efforts, $8.1 billion has been returned to MF Global customers and creditors,” said SIPC President Stephen Harbeck. “I commend MF Global Trustee James W. Giddens and his staff, and Judge Martin Glenn of the United States Bankruptcy Court for the Southern District of New York, who made this excellent result possible. The end of the MF Global liquidation demonstrates that the law designed to protect customers of failed brokerage firms works and works well.”