I think the difference is that Google is a lot less likely to infringe on employees' right to bear arms than they are their right to organize, especially given that this message literally appeared on a website of a firm Google hired specifically to suppress organization
I have a poster here in my home office that was mailed to me by my employer's HR department. It advises me of all my rights under state and federal labor laws: equal opportunity, workplace safety, minimum wage, etc. In my mind, it is not at all inappropriate to advise employees of their rights. In fact, the only reason I have this poster is because state and federal labor laws require such notices. Those laws and those requirements are written in the blood of all the serfs, children, and laborers who couldn't earn living wages or who were forced to work at a tender age or who were injured due to corporate malfeasance. The freedom of association is likewise recognized as a right inherent to all people, and its protections were likewise bought with blood. We should all be reminded of our rights and the reasons we safeguard them. An employer who tries to interfere with its employees' freedom of association only seeks to exploit them. If it treated its employees well, it wouldn't need to worry about organized labor—and its employees wouldn't need to organize in the first place.
