Are corporations people?
The answer to this question depends on the meaning. I won't get bogged down in the metaphysical definition of person. There are 2 different possible meanings to this question and we need to address which meaning we intend to convey.
The first meaning is that a corporation is a person separate from all human people and created at the time of incorporation. When people on the left say that corporations are not people, they are I hope referring to this meaning. Legally, a corporation is a person in this sense.
There is a second sense in which a corporation is people. A corporation is a group of people coming together for a common goal. Some corporations produce goods, others services. The corporation is made of managers, workers and shareholders.
When I say corporations are people, I mean it in this second sense. The issue of corporate personhood comes up in several contexts. Corporate taxes are not paid by some soulless nonperson but by the individuals who make up the corporation or by the people who buy the goods and services made by the corporation.
In the same sense, when the corporation says something, it is not a personless entity making unprotected speech, it is a collaborative effort by the people within the corporation exercising their right to free speech in a collective manner.