The abstraction of "infidelity" does not have a place in certain types of minds.
It doesn't register.
There is no place to consider "OK" or "Bad" or "WTF?"

Those of us that do have that place in our minds to consider these sorts of abstractions are puzzled by those that don't.

Consider how NC Lt Gov Mark Robinson's email address was registered on Ashley Madison.
It doesn't matter to him.
Nor to his supporters.

It
Doesn't
Register.