In order to divest themselves of investments, the leftists will have to sell their holdings. Others will buy them, so I'm not sure how I see that it will hurt the companies in the long run. In fact, if the leftists are intent on getting out quickly, they may find that THEY lose money. (A good thing in my view :-)
The value of the companies is in their products and services and there are plenty of folks who will recognize that and support them. They may be better off with stockholders who believe in their products and services, rather than leftist investors.