He can, and did, voice his opinion on social media. He was not prevented from doing so in any way. Other people read his opinion and decided they didn't want to work with him anymore. Also their right.
Because enough customers and partners decided they didn't want to work with him anymore, he felt like the only way to save his business was to step down.
> Should this very large group of people not be employable because of this opinion
It's not just an opinion, but legislation that puts millions of women at risk. If you support things that are harmful to women, I don't see why I'd employ you. :shrug:
For what it's worth, this is what conservatives have been pushing for decades, the ability to discriminate based on skin color, sexual orientation, and political beliefs. I am all for giving them their wishes on this one.