Is dietary fiber really essential for a person?

What do you mean by "essential"? If you mean "essential for good health" then the answer is "yes". Failure to get enough fiber can lead to a number of health problems, ranging from constipation to serious issues such as diabetes, cancer and cardiovascular disease.

No and neither is a diet of spam.

I've heard spam has a lot of fat in it.

and it's not Kosher, either.

That's one reason why SPAM is good for brain matabolism.

Isn't "fiber" what used to be called "roughage"?

Once upon a time hemmorhoidectomies were sometimes done to get rid of a bothersome hemmorhoid. Then along came the concept of fiber. Today, I believe, many a hemmorhoid is treated "early" with eating more fiber. I am not sure why it works? Perhaps, the anal sphincter muscle relaxes when it feels needed, more often?

looks like someone could use a can right now