Corporations, just like a group of concerned mothers pooling money for a billboard, are a grouping of people. And shareholders have rights to spend their own pooled money on speech, just like the mothers have that same right.
This is disingenuous - a group of concerned mothers does not have a government-created liability shield, for starters.
In general, shareholders are always able to pool their money directly in the manner you are stating. This being uncommon shows that the situations are not equivalent.
In general, shareholders are always able to pool their money directly in the manner you are stating. This being uncommon shows that the situations are not equivalent.