Nobody is talking about annulling free speech rights, the issue is granting extra free speech rights to entities that are not people, as well as considering activities speech, and therefore protected, that are not speech. Like donating money to political campaigns.

People can still donate their money, but to allow corporations, which are explicitly created to concentrate money and power, to donate money to politicians, that has a massive impact.

The people working for a company can have free speech without the company itself having free speech. In fact, some companies having a tendency to curb free speech through contracts denying people the right to talk about certain things.

And then there's also the issue that corporations get used to dodge personal liability by their owners and employees. If corporations don't share their people's responsibilities, why should they get to share their speech? Corporations are very explicitly a separate entity, and not merely the group of people working for it.