In the US this would be 100% legal. For almost all jobs, you can fire someone for any reason (I don't like your shirt, your jokes weren't funny, it's a Tuesday) or literally no reason at all. The exceptions are few and far between - unions provide additional protection via collective bargaining agreements; you can't fire someone for being in a protected class (i.e. because of their race or gender); and you can't fire someone in retaliation for something like a wage complaint. You could almost certainly fire someone for making a video you don't like (unless they're in a union, which is very few tech employees.)
While it is true that most employment is “at-will” (which means that both sides voluntarily choose to employ/be employed) for both sides, in a friendly employee state like California, there are numerous wage claims and employment law suits that come with doing business. It’s not as easy to fire in some states.
