I agree with you that I don't look to Lewis for his take on geopolitics. However, I think you just have to accept that in the body politic there are many people (a majority in all likelihood) who have a say in their democracies but don't concern themselves with situations such as Israel-Palestine.

Lewis has the attention of these people, and he feels he's doing the right thing by bringing attention to the plight of innocent civilians in the region. If his post has inspired at least one person to be more aware and sympathetic to the human suffering, then hasn't it been worth the effort?

He's allowed to have an opinion and voice it

What does that have to do with the post? Maybe he voiced his thoughts unprompted. Also, whether we like it or not, celebrities have influence. That's why their takes are important. When a bunch of celebrities support a cause, that cause will get a lot more media attention and public support in the form of donations and such. It's also why it's ok to "cancel" shitty people. Because if you don't, they'll just normalize that way of being by swaying people to their side.