The Humanity of Marriage
If quality marriages were about minimizing differences then incest among identical twins would result in the best marriages.
Obviously, that’s absurd. What really matters is not similarity but compatibility. We all belong to the same species. Therefore, all sort of people can successfully procreate and live a happy live.
Of course, there are some differences that render individuals incompatible. I am glad, for example, that Gordon Hinckley has ended the practice of advising gay men to marry women. Gay and straight people can be compatible in many ways but marriage is clearly the exception.
Beyond sexual orientation, most other differences are not valid reasons for marriage prohibitions.
Philosophically, racism is the notion that one kind of human beings should not breed with another. Dog breeds, for example, require that saint bernards do not breed with German shepherds or Newfoundland dogs.
The very suggestion that rich people should not marry poor people, that smart people should not marry stupid people, or that different ethnic or religious groups should not intermarry establishes racism. Those prohibitions deploy the same logic as the statement that dachshunds should not procreate with poodles.
On average, of course, it may be perfectly true that any dimension of difference may lead to greater divorce rates. However, averages do not manifest themselves in the lives of particular couple.
To any couple, the probability of divorce is either 0 or 100%. You either get divorced or you don’t.
Couples need to assess their compatibility for themselves. In many cases, they will be perfectly fine.