The workings of people and corporations part ways at the bottom line, which you must know full well.
An individual will always represent his own point of view, more or less. A corporation does not represent its employees politically. It often does not in fact represent its shareholders politically.
This disconnect in voices is multiplied by the power multiplier of the profits brought about by many, fueling a voice which speaks for the few.
It is not the group-ness per se which is the fatal flaw in Alito's reaosning, but the misrepresentation in political matters, especially elections. The equivalency of money and speech, or speech fueld by money as distinguished by speech fueld by individual thought, is the great lie in the SCOTUS rationalization. Once having slipped this lie into the works the entire facade of the First Amendment argument becomes a shambly hollow pretense.