“Professional investors have ample opportunity to sin—and face ample rules that aim to prevent them from doing so. Without doubt, their investment practices can be unethical. Retail investors face far fewer potential perils. One possibility, though, might be the internet-enabled practice of collaborating to damage a stock’s price. Permitting short-selling appears to be a public good, by improving market efficiency. But, to my knowledge, there is no evidence that society benefits from times when the activity is conducted collectively. It may even be harmful.”

[COMMENTARY] What are the ethics of selling short a stock and then gaining massive publicity on the web to encourage others to similarly sell short the same stock? Is that ethical? What about the opposite? Do you buy a stock and promote that stock as a buy all over the web? So is that ethical? The point is that markets are full of both buyers and sellers and all are promoting their particular views. Hence, I would say neither promoting a buy or sell is unethical. However, doing so when you do not believe in your action, that, I would define as unethical.
Where Is the Line Between Ethical and Unethical Investing? By John Rekenthaler, June 1, 2023, Morningstar, USA.