I think the difference that I do not see fully considered is the expectation of someone's preferences being something someone else has a right to expect to be c

I think the difference that I do not see fully considered is the expectation of someone's preferences being something someone else has a right to expect to be changed, with the causes of the preference (in this case an attractive partner) being somewhat beside the point. This is why as the author points out "it’s easy to see that cuter kindergartners aren’t entitled to a better educational experience". In that role the teachers job is to teach students, with her personal preference in students coming in to play being undesirable. Relationships on the other hand are only between two people and what they like about each other, and their own feelings. Otherwise this line of reasoning can be taken to some potentially rather strange places. Is it then discriminatory for example to exclude partners based on age or gender? These would seem to meet the qualifications of control, harm and unfairness.