There's so much confusion and emotionalism about discrimination that I thought I'd take a stab at a dispassionate analysis. Discrimination is simply the act of choice. When we choose Bordeaux wine, we discriminate against Burgundy wine. When I married Mrs. Williams, I discriminated against other women. Even though I occasionally think about equal opportunity, Mrs. Williams demands continued discrimination.
You say, "Williams, such discrimination doesn't harm anyone." You're wrong. Discriminating in favor of Bordeaux wine reduces the value of resources held in Burgundy production. Discriminating in favor of Mrs. Williams harmed other women by reducing their opportunity set, assuming I'm a man other women would marry.
Our lives are spent discriminating for or against one thing or another. In other words, choice requires discrimination. When we modify the term with race, sex, height, weight or age, we merely specify the choice criteria.
Imagine how silly, not to mention impossible, life would be if discrimination were outlawed. Imagine engaging in just about any activity where we couldn't discriminate by race, sex, height, weight, age, mannerisms, college selection, looks or ability; it would turn into a carnival.
I've sometimes asked students if they believe in equal opportunity in employment. Invariably, they answer yes. Then I ask them, when they graduate, whether they plan to give every employer an equal opportunity to hire them. Most often they answer no; they plan to discriminate against certain employers. Then I ask them, if they're not going to give every employer an equal opportunity to hire them, what's fair about requiring an employer to give them an equal opportunity to be hired?
You say, "All right, Williams, discrimination in marriage doesn't have the impact on society that other forms of discrimination have." You're wrong again. When there is assortive (non-random) mate selection, it heightens whatever group differences exist in the population. For instance, higher IQ individuals tend toward mates with high IQs. High-income people tend to mate with other high-income people.
In other words, if high-IQ people were forced to select low-IQ mates, high-income people forced to select low-income mates, and highly educated people forced to select lowly educated mates, there would be greater social equality. While there would be greater social equality, the divorce rate would soar since gross dissimilarities would make for conflict.
Common sense suggests that not all discrimination should be eliminated, so the question is, what kind of discrimination should be permitted? I'm guessing the answer depends on one's values for freedom of association, keeping in mind freedom of association implies freedom not to associate.