I believe the objection is that "Christening" appears as a basic fact and it is a Christian ceremony so exclusive of other cultures, so why not have the options for Namkaran, Aqiqah, Brit Milah etc?
The objection is deeper than that. Christening appears as a basic RM fact and Christening (by that name) is not even embraced by all Christian cultures. In some Christian cultures it is not practiced at all and in other Christian cultures a similar activity is practiced for infants but it is called Baptism.
Irrespective of one's own religious beliefs and culture, many genealogical records are religious in nature. So I think you have to use and interpret data the way it is found. For example, I am neither a Quaker nor a Lutheran, but I make heavy use of both Quaker and Lutheran records from the Shenandoah Valley from the 1700's. I record the data as I find it, and Quaker dates are in what I consider to be an unconventional format. Similarly, there are church records that may be called Christenings OR that may be called Baptisms, which are events for infants which may be the best indication we have of when someone was born. I think we as genealogist should record such data the way we find it. And in the absence of a birth fact, it should be possible to use EITHER type of infant religious record for estimated age calculations for life events. We shouldn't have to call something a Baptism if it was a Christening in the records, and we shouldn't have to call something a Christening if it was a Baptism in the records.
I personally prefer also to add a birth fact for everybody, which solves a lot of the problems. For example, if I have a Baptism on 28 Feb 1704 which I know to have been an infant baptism, I might enter a birth fact with a birth date of "estimated 21 Feb 1704" with a note about how the estimate was made. Even better might be if I have a Baptism on 1 Feb 1704 which I know to have been an infant Baptism where I could enter a birth date of "estimated Jan 1704". But I respect that some users prefer not to enter a birth fact without explicit evidence for that birth fact.