most of this only applies to social media companies. there are business models, even in tech, that simply don't revolve around user-generated content. but yeah, if you host mass UGC and have moderation, you can't really escape the political implications.

> How do you deal with employees expressing their opinions at work?

have a policy that work comms are only for discussion of work-related topics. keeping politics outside the permanent record is probably beneficial for everyone, and people are usually less nasty in person anyway. you'll probably end up with only a handful of employees who routinely start arguments over non work-related topics. after a couple warnings, it's time to "separate" them from the company.

> There are right and left-wing plans (birth control etc).

this is currently not an issue for the company. per ACA, employers are required to cover birth control in their health plans.

> The holidays are comming. Do your employees say "merry christmas" or "happy holidays"?

I really don't believe many people care about this. I work with people of every major faith, and it has literally never been an issue. if you want to be extra neutral, you can get rid of company holidays and just give everyone a little extra PTO. this way the company doesn't have to play the delicate game of deciding which faith's holidays to recognize.

tl;dr: I don't think any of this stuff is terribly hard to sidestep. many tech companies choose not to; I suspect they feel they benefit from playing the game.