True love would hardly be so cruel.

What if John's mother has disagreeable peculiarities?
She is none the less his mother, and, as such, he is bound to love and respect her.

If the love he bears her blinds him to her deficiencies, is it not the part of a true wife to keep his eyes closed to these foibles, since seeing them will make him uncomfortable?
Every man likes to feel that his dear mother and dearer wife are congenial friends.

And it is their duty to be friendly, if not congenial.
The mother-in-law, too, has her task.

It would be folly to state that she is not often and grossly to blame for the uncomfortable state of this relationship.