It's only natural that some people employed at the same workplace would end up getting romantically involved, and there's no good reason why a company would need to stop that. Significant problems with romantic relationships in the workplace usually only arise when one party is of higher status than the other, and this should type of romantic relationship should be the only one barred by companies.
You will usually form some type of bond. It probably happens more times than most people know. As long as people keep it professional, then companies should have no problem with it. Of course, most companies do not allow fraternization, but does it really work? So they might as well just allow it, and let people know to behave.
A romantic relationship is not a relationship that people are expected to report on to anyone unless they make the personal choice to. There is no reason an employer should be involved with making the choice to become romantically involved with someone. If employers are concerned that a romantic relationship will distract employees then they need to address the incident, not the relationship. If a person is spending too much time talking to their romantic partner, the problem is the excessive talking, not the romantic relationship. Personal relationships are of no business to an employer and employers should not be given the power to ban such relationships.
The question is not should companies allow it, but the adverse, should companies NOT allow it. By companies not allow it undermines different rights granted under the constitution. However, by a couple becoming romantically involved at work, they have a responsibility to the company, in that their romantic relationship should NOT undermine the chain of command. If that happens, then the company will (and should) take an interest in it.
While companies shouldn't encourage such behavior, I think companies shouldn't disallow such actions from taking place. A company and work place should not prohibit people from partaking in such social matters as long as it does not affect their jobs. I think that there is some problems that can happen due to such relationships, companies should take care of it differently.