I confess I don’t really understand the “narcissism” take on this behavior. To some people, a particular given name is a marker of family belonging, not merely a personal identifier.
When Margaret Smith or William Doe follows a family tradition of passing on their first name to their child, they’re generally not thinking “wow I am the awesome Margaret or William, and I shall name this sprog Margaret or William as a testament to my awesomeness!” They’re thinking about all the previous Margaret Smiths or William Does who passed the name down to them, and wanting their child to be part of that heritage.
I suppose if the parents don’t have such a family naming tradition and really are naming kids after themselves just as a self-testimonial, that would be rather narcissistic. But I’m not sure I’ve ever encountered such a case in real life.
I mean, giving your kid your own name is not really comparable to the admittedly egotistical practice of sticking your name on other objects and entities specifically to commemorate yourself, as in “The Margaret Smith Auditorium”, “The William Doe Oncology Center”, or even arguably “Stark Enterprises” or “Trump Tower”, “Trump University”, etc.
Those acts of naming are centered on you, the individual person. But when you give your name to your child, you are sharing that name with an entirely different individual person. To me that seems fundamentally different.
So when I meet, say, a William Doe IV* I don’t think to myself “Gee, what a narcissist ol’ William Doe III must have been to give his son that name”, I think “Huh, looks like this branch of the Does has a strong family tradition of patronymy”.
*(asterisk) And yes, I concur with Miss Manners in preferring the “reset” generational numbering system where your number or title (as in “Jr.” or “Sr.”) depends not on your chronological place in the overall sucession but on your chronological place among the current holders of the name. So the eldest living William Doe is just “William Doe”, while his son is “William Doe Jr.” and his grandson is “William Doe III”, etc. But if I meet a William Doe IV whose family prefers to use the “permanent” type of generational numbering, where William IV will be William IV forevermore even when he’s the eldest living William Doe in the family, I don’t try to argue him out of it.