I said eventually, because not every belief is going to come up at once, and I said probably because not every belief in the set of religious beliefs is toxic or wrong.

The belief may be true in some sense, but its underlying reasoning will need to be adjusted.

You are correct though that the basis of most (almost all) religious belief is outright crazy and needs to be opposed as soon as it is encountered.

As an example of a belief I am describing:

Render unto Caesar those things which are Caesar's and unto God those things which are God's

The only thing wrong with this belief is that the set of things in the second category is empty, and the set of things in the first category needs to be adjusted based upon that second category being the empty set.

Thus, this is an accurate belief. Vacuous for the most part, but accurate. It should be amended to just

Give people what they are due.

(Edit: What Eliezer is describing in his post on the Sin of Underconfidence is a phenomenon called the Dunning-Krueger Effect)