First of all, let’s remember which claim we’re addressing. We are talking about your adamant claim that religious conversions are rare. We are not talking about whether the majority of believers experience conversions or not. We are not talking about whether the percentage of conversions exceeds 50%, or even 25%. Rather, we are addressing your specific claim that “People switching religions from what their parents practice is actually pretty rare” (emphasis added). It isn’t, and your own cite demonstrates this.
First, let’s look at your cite. No offense, but it’s pretty obvious that you didn’t take a good close look at those numbers. Your own cite says that 71.8% of Southern Baptists, for example, remain within that denomination. This means that nearly 29.2% of them decide to adopt different religious beliefs. 29.2% is admittedly less than a 50% majority, but it’s hardly “rare.”
You get comparable results for other denominations. For example, by your own statistics, the United Methodists and the Presbyterians change their beliefs with greater frequency. Heck, among interdenominational Christians, the actual conversion rate is 52.9%! In fact, the lowest conversion rate occurred among Mormons, and even then, fully 9.2% of them abandoned the teachings of their parents – a relatively small number, but far from rare!
Moreover, this study would still underestimate the frequency with which people adopt beliefs that differ from the ones with which they grew up. There are multiple varieties of Presbyterianism, for example, yet this study treats them as a monolithic block. Similarly, there are a great many interdenominational churches with varied beliefs, yet this study fails to account for people switching from one church to another. Heck, it doesn’t even account for people who choose to remain within a given denomination, yet whose beliefs have nevertheless changed.
As I said, I doubt that you can find any strictly scientific data for the frequency with which people change their beliefs. One thing is for sure though – the data which you cited doesn’t prove your point. Quite the contrary; it demonstrates that these conversions are NOT rare – and that’s even without accounting for the fact that it doubtlessly undermeasures the number of these conversions.