[Avodah] Only Torah Judaism

[Professor Levine]

At 04:37 PM 5/30/2022, Micha Berger wrote quoting an anonymous source:

>If someone with a Jewish mother was raised Baptist, or ch"v joined
>a church (maybe j4j) and wanted to return, we would expect geirus
>lechumerah. A ritual "only" with the weight of minhag, of going to the
>miqvah befor we consider the person a Jew in good standing, who (if male)
>could be counted for a minyan, whose testimony is valid, etc...

I do not understand this assertion about expecting "geirus 
lechumerah."   If his or her mother was Jewish, then my understanding 
is that he or she is Jewish without question.

Am I missing something here?

Yitzchok Levine