You have been reading too many memes. Citizens United does not say money is speech.

Citizens United says specifically that when a bunch of people take their money and get together and start a new corporation (Citizens United) (a not-for-profit corporation in this case, though not a charity) and the corporation proceeds to engage in political speech (by filming a movie named Hillary: The Movie)...

then the corporation, as an entity, is considered to have the rights like the right to free speech, because it is owned by people who have rights, and this is a way for those people to exercise those rights together. Therefore this political speech is protected by the First Amendment, and restrictions on it are evaluated on the standard of strict scrutiny, and the FEC cannot halt this distribution just because the corporation was using money to make it happen.

(You will notice that people are not allowed to band together and exercise the right to vote, and thus corporations don't get to vote.)

The financial system has _many_ guard rails including licensure (see the FINRA exams), regulations and regulatory bodies, and orders to halt or limit trades and positions on volatile securities.

This concern is relevant to GME, BB, AMC, etc. because folks are joining Robinhood, Webull, and similar apps in record numbers in a rush to jump in on these hyped-up opportunity.