Depends on context. If (say) Argentina invaded the Falkland Islands again, then the UK declared war against Argentina and launched a major military campaign against them - would you expect your employer to be cool with your vocal support for the Argentine side?
You seem to have pivoted away from the original point you were making, which was why the employee was working at an Israeli company if she disagrees with actions of the Israeli state. But to address your new point:
Being "cool" with it is a different thing from firing me for it. I'd expect my employer to form its own opinion which might differ from mine, and I'd reasonably expect my employer to dictate what I can express while I'm representing them (e.g. while speaking to customers, or posting to the company website).
I'd also expect them not to get involved in my private life and to respect my rights under the Equality Act 2010; specifically Section 4 (belief is a protected characteristic), Section 13 (discrimination = treating someone less favorably than others based on a protected characteristic), and Section 39(2) (discriminating against someone by dismissing them is unlawful discrimination).
