Why work for someone or something that you don't believe in?
I get it that many people have limited choices in life, but the readers of this forum are typically of a talent level that allows them to have more of a choice.
Don't stay working at a job you don't believe in. Life is too short.
I later realised that it only made sense to invest in every company you work for.
I also was very disappointed that someone never gave me this advice, and instead I got the opposite advice that my actions don't matter. The same advice that you are trying to give now.
It was bad advice then, it is bad advice now, and it is the wrong advice for this audience.
The number one rule with investing is diversity.
It's not like you would invest your entire portfolio with your company, so why you think it's overly concerning to invest even a small amount with a company you are intimately familiar with is beyond me.
inflated stock price through extra demand -> more wealth for major shareholders
https://www.google.com/search?q=uaw+historic+win (for example)