I find this a seemingly straight-forward point I've never gotten a religious person to acknowledge.

because they don't see it that way, they have their own understanding of free will, religion sells itself as test ( for the most part ), if you pass the test ( temptation or whatever you wanna call it ) you're qualified to enter heaven, so in a way even if you're born christian or a Muslim you still going to get tested, so in their view it doesn't change anything, but from our perspective, it changes everything because we bet that if their parents didn't make them that way, they would never go that route on their own...

99.99999% of people follow the religion they do because their parents did. Not because it's true. That Christian, that Hindu, that Jew. It's just because they were told it was true at birth.

That's why we must address the root cause of all this, which is religion, in Islam for example "Prophet" Mohammed piss be upon him, said

“Every child is born in a state of fitrah, then his parents make him into a Jew or a Christian or a Magian.” (Agreed upon)

As you can see, Mohammed doesn't apply his own observation on his beliefs and because people glorify him, they will never dare to question his reasoning, which is also their own reasoning now..

You can tell a religious person to criticise everything and everyone, and they can, tell them to redirect their critism to their own belief, and suddenly they'll become intellectually handicapped

I wouldn't make it that high. A large amount of Christians I know of are converts.