Addition to my post above: I should reference one of C.S. Lewis's very negative--and, I think, very silly--statements on other religions. I'm not sure where the reference is, but it's probably Mere Christianity. He says that you don't have to consider all the worlds religions, you can just group them into different types. He goes on to dismiss the Eastern religions and then to say insulting things like "all that was best in Judaism and Platonism survive in Christianity."
Honestly, I find sentiments like these so laughable that it's almost hard to take offense. And they're generally spoken by people who don't go to the Seders of their Jewish friends, or Shabbat dinners, or the Torah studies at their local synagogues. In my view, people of different religions have lots to learn from each other--but you wouldn't know it from Lewis's careless remark.
He may have grown less careless as he went on. Moreover, I did read somewhere that when one of his step-sons wanted to practice Judaism, Lewis went out of his way to find a kosher butcher, which was no easy task in his area. (Both his stepsons are are halachically Jewish--that is, Jewish according to Jewish law.) If I'd been a neighbor and anyone had asked me, I would have told the kid just to keep dairy kosher so he didn't have to make his step-father's life difficult.
But, if the story is true, Lewis certainly did right by the kid.