This leads me to believe that this inculcation of which you speak is not nearly as effective as you make out.
Do you mean bringing up kids as religious as a means to ensure they are religious as adults. If so, yup you are right it is pretty ineffectual, with (in the UK) nigh on 50% of kids brought up as religious rejecting that religion when they are adults.
The issue isn't whether it is effective, the issue is that it is absolutely necessary as kids brought up in a non religious household almost never become religious as adults.
So a religious upbringing is necessary for someone to be religious as an adult, but not very effective (i.e. many will become non religious as adults).
A non religious upbringing is hugely effective at producing non religious adults (virtually all will be) but not even necessary as there are plenty of non religious adults that come from religious upbringing.
And of course most religious upbringings specifically use all sorts of approaches to inculcate religion. A non religious upbringing typically does nothing to inculcate non religiosity, it merely doesn't involve religion.