You raise two separate issues: Diversification and divestment.
The opposite of diversification is all the eggs in one (or a few) baskets. I didn't watch the video but I'll note that Warren Buffet won his million-dollar bet by buying Vanguard's Whole-Market Index fund. Also, "investing for income" involves weighting heavily toward bonds. They don't grow for the future, but they provide a steady, reliable income. Picking individual stocks is a highly risky business. Mutual funds keep that risk much lower, and indexed funds keep both the risk and the cost at a minimum.
I totally agree with you on divestment. However I am too cynical to put my retirement income at risk by trying to manage my own portfolio in individual issues. And I would not trust any investment manager to do it for me. (I do have an investment advisor who advises me on mutual funds, mostly bond funds, widely diversified.) There are some funds that claim to be "socially responsible," but frankly I am not going to over-weight myself in any of them. And honestly, if I were not so hypocritical about my principles, I would divest myself of TSLA for Musk's abysmal treatment of employees and his anti-union stance. Once upon a time I would not have touched an anti-union company. But my cynicism has won out and I bought my Roadster and then my Model 3 in spite of my principles, because I wanted an electric car so badly, and for all Musk's horrid actions, he makes the best cars on the road. It's hard to find a "good" company. Amazon, for example, has superb customer service and fast delivery, but treats its employees like dog doo. In the end, if you're concerned about the environment (which I am) and the rights of workers (which I am) there's no company you can support with your purchases or your investment.
So I drive my electric car, and run my home and my car on solar, and pay people who do work for me (my landscaper and my house cleaners, etc.) a fair wage, which is about 50% more than they ask, but I'm not going to risk my income by attempting to manage my portfolio in individual issues.
Sorry for the long-winded reply.
tl:dr: Managing a portfolio in individual issues is highly risky if you know what you're doing, and foolish if you don't. Divestment is the moral choice, but in this economy, no company would meet even minimal standards.