I think where that saying comes from has some merit. If your self-esteem is very, very low, it's hard to believe others can love you. Which makes a loving relationship difficult. It can lead to someone not being able to open up, to make themselves vulnerable because they view themselves so unworthy. It also can make one desperate in some respects. If you do not love yourself, yet have love to give, you will be desperate to find someone to give it to, which can lead to bad relationships as well.
It's not black/white, but self loathing is generally not attractive to many people. And the ones that are intrigued by it would be a mess their own selves and you never know what you're getting there.