First, the Viking Answer Lady provides us with some background:
One reason why love poetry was so ill-regarded by the Vikings may have been due to the fear in pagan times of magical ensnarement of the woman so immortalized by the power of the verses (Foote and Wilson, p. 112).If you believe that Odin has the ability to seduce a woman with a song/runes/poetry (see Runic Superpowers of Odin Part II), and the gods have been known to pass the magic of the runes on to mortals (Heimdall as Rig teaches Rune magic to his son Jarl), it makes absolute sense that other mortals might be concerned about magical ensnarement of their daughters in every day life. How can you be sure that a poem is just a poem, and not a spell meant to seduce your daughter and ultimately dishonor her? How can you even be sure that the person writing the poem isn't Odin, for that matter, or worse, Loki, who is also known for shape shifting, come to take advantage of your daughter/sister.
And I have to say, it makes absolute sense for love poetry to have been a much, much more serious concern to a culture with a god like Odin, and in particular, a god like Odin to whom poetry is pretty much the source of a lot of his wisdom and superpower via the runes. When Poetry is that powerful, it only makes sense that its use would be governed by law, and as defensive as Norsemen can be about their women, the law is there to protect more than just the female party.
It might seem kind of absurd to us, but poetry was magic according to Norse society -- we see that clearly in the Havamal when Odin talks about his magical powers:
152.WORDS have power over the minds of men. And it isn't just the gods who can wield them in persuasion. I think that's a lesson we, in all our practicality, seem to have forgotten.
An eighth I know: which all can sing
for their weal if they learn it well;
where hate shall wax 'mid the warrior sons,
I can calm it soon with that song.