As someone who was raised Catholic and married a Jew, I can only shake my head at this one. I remember how upset my mother-in-law got when she found out my oldest had been baptized (a couple of years after the event). But I think this probably has more to do with the idea that Jews have a duty to maintain their tribe by raising their children as Jews, rather than any specific aversion to other religions. (Although I have to say, my own in-laws were pretty bigoted and uninformed about Catholics.)
I had my first son baptized without giving it that much thought. It was just one of those ritual things. By the time we had the second kid, we had a ceremonial bris performed – but without the party, which also pissed off my in-laws. Oh well! (My mother-in-law was also pissed that I wouldn’t take the kids to Hebrew school. I told her that her son was more than welcome to do so, but I didn’t see it as my responsibility. I said something to the effect of “If you really wanted Jewish grandchildren, you should have raised Jewish children.” Once they were bar mitzvahed, my husband and his brothers lived a completely secular life – until my kids arrived, and then suddenly, it was an issue.)
I always felt a little bad that my kids weren’t raised with anything but now, not so much. Because I don’t believe in religion. I’ve seen it used primarily to build walls and divide people, and since I believe we’re all one, organized religion is a contradiction.