I think "Revenge of the Sith" answered this question, Love makes us do dumb things, anyone who has ever been in love knows what I am talking about, as in "Sith" Yoda explains it clearly>>> "The fear of loss or attachments is a path to the dark side" to qoute him from "Phantom Menace" >>>> "fear leads to anger, anger leads to hate, hate leads to suffering".... as demonstrated in "Sith", this is why I have never understood those who hate EP I, seeing Anakin as a innocent kid made his turn in "Sith" all the more powerful & sad!!!, If Lucas would have began with "Sith" I doubt the impact would have been the same!!
I see. My half-sister also thought it would also distract them from their duties, I guess. I thought that was nuts. That was why the Jedi population was limited. Was that romance restriction used in the original trilogy? No.
I think that non-attachment leads to a lot more suffering than loving someone and being loved. I wonder what the rate of child molestation is in the Jedi order? Perhaps its on a parallel with the Catholic church.
Personally I think the entire thing is stupid. I fail to see how caring about somebody or forming an attachment to them leads to the dark side. Sure you can go on about the whole attachment to jealousy to anger to hate thing all you want, but I think the answer to the question lies not in forbidding attachment and love, therefore leading to the inability to go to your superiors or those around you about your problems, to help you, so you end up having to bottle them up and eventually they are let out in an unhealthy manner, that's what leads to the dark side. The answer is to teach how to accept the loss of those you love and deal with your more volatile emotions instead of suppressing them.
This is a no brainer. Romantic love is forbidden due to its attachment. George Lucas based the Jedi on Tibetan Buddhist monks. Remember, Episode V - Empire Strikes Back - where the city in the clouds - Bespin- is a Tibetan gas mining colony. (Note - The city of Lassa in modern day Tibet is sometimes referred to as the City in the Clouds).
Also Yoda's musings in Episode 1 where he tells Anakin that fear leads to anger; anger leads to hate and hate leads to the Dark side. This is straight Buddhism.
I am currently studying gnosis. We carefully observe attachments because most attachments stop us from self realising. There is nothing wrong with love. that is divine love or love for all humanity, BUT, romantic love has the dual elements of fantasy and selfishness.
It is the selfishness of attachment that leads Anakin on the dark side as he is "scared" of losing Padme. Anakin marrying Padme from the Force point of view in effect meant that Anakin had dissolved his Jedi vows (you cannot serve God/The Force as well as his opposite in this case the Dark Side/Emperor). In the novel Attack of the clones the Emperor "grimly smiles" when Anakin marries Padme knowing full well that the Vader persona was being rapidly created. Palpatine encouraged the ill-fated union knowing it would "cut" any links to the Jedi order.
It is the same for the Jedi and for the Sith. The Jedi are selfless by NOT forming emotional attachments. The Sith are selfish and power mad. A love interest would distract them from their ultimate goal .... power. Palpatine/Emperor tells Anakin this in Episode III just before he recites the story of Darth Plageuis the Wise is told.