That was the reasoning I heard as a boy, that was common in religious families, ergo among almost all Irish families, since the women especially were religiously observant.
Just making up a name, or using one from a commercial product, is to make a mockery of this.
The manipulative naming motive I mentioned above would certainly seem to qualify as mockery. However, there are some unconventional names that are part of frontier tradition. Some rural families got into the habit of giving children made-up "family names" (as they are called) and passing them along from generation to generation. Examples given in a newspaper article I saw years ago were "Lebus" and "Orem". I personally know a young woman named "Thamer", who went by a nickname at the office rather than have to explain her unusual name to people. She did this for several years, then changed her mind and let everyone know to call her by her given name, which we do now.
Another example is the former NFL Oilers football coach O.A. "Bum" Phillips, father of Wade, also an NFL coach. "Bum" was the old man's nick, his given name being Oail, a "family name".
I suspect the names may have been surnames (last names) of other relatives, pressed into service as first or middle names. Nothing wrong with that. Again, the idea is to both honor the descendent and to try to imprint on the character of the child. "Prescott" is not a normal Christian saint name, but it was the last name of a Bush family patriarch. It's the middle name of George P Bush.
SD