I think I know various places this came from.
Start with being Lebonese. Given what Israel has done to Lebanon over the years you have a big base of anger building up over the years. Does not justify her point of view, but it is rather like some Jews I grew up with who hate Germans, and would not listen to Wagner or buy VWS or eat bratwurst. If enough of your relatives are killed by another nation, it is possible your anger won't stop with their government. Really not that different from the emotional thinking behind the Israeli blockade of Gaza.
Another thing that may have contributed to this is the whole culture of journalism. There is this whole false objectivity thing where journalists are not supposed to have opinions. But of course people have opinions, so all that means is that the opinions are there but unvoiced. Which means that since the opinions are unvoiced they can sometimes fester and mutate in the dark, because they are never brought into to the open when comparatively small and harmless and properly mocked.
I've seen cases on this board where someone brought out a comparatively mild anti-Semitic comment, or mildly homophobic opinion, without on this board. And they were called out on it and realized they had absorbed bad attitudes without realizing it and corrected themselves. And journalism kind of helps condition against it.
And I'm fine with Thomas being fired for this, and to me it really does not undo all the great work she did before. She did something wrong, apologized and took the consequences. But I'd like to see it applied to Glen Beck and to every journalist or politician who wants to repeal birthright citizenship. Demand apologies from all of them and then fire them regardless of whether they apologize or not.