I know generally we tend to side “against” the employer on many issues. However I believe this is one example where it actually protects both the employees and the company by helping to prevent hostile and toxic work environments caused by close work relationships. In a perfect world where everyone is a mature adult and all relationships work out or breakups are handled well then maybe something like this isn't necessary. However from my perspective I do not trust most people to handle these situations correctly on their own.
I understand these policies aren't very common so I even asked why a lot of companies don't have them. It seems that most people consider it too much control without looking at the bigger picture that it helps the employees as well. People are also used to work relationships so they think they should be common and allowed just because they got lucky and it worked out for them. I find it's very difficult to get more objective opinions on something like this because everyone is biased especially if they're never been in a workplace that has a similar policy. We're not all stoic statues we just don't see a reason to have that kind of additional risk when regular work is stressful enough.