Aha. So it's gay marriage again?
The western, juidicial process of creating laws is a matter of reason, first and foremost, not morals. You can go to Iran if you want a strong, moral state.
And secondly, good laws are also meant to be logical, coherent and hopefully as small as possible (sadly that's more a bonus today, but still).
That explains for instance, why the condemnation of (especially moralic), victimless crimes died out in the western hemisphere one by one.
While striving for a free society, the state should carefully balance along that line of freedom vs reasoning.
Until some time ago, that meant that you're free to marry a consenting adult of the opposite sex. Before that, you'd have to ask her owner (the father) beforehand. Before that, her clan. Before that, depending upon culture, you may even had to rob her.
Note that "love" plays zero significance here, as today.
Today, there might be fourteen year old, adult (in a sense that they are mentally and sexually fit) girls who'd willingly marry someone. We forbid that.
So why on earth did we go backwards with this detail, gettin more and more liberal generally but actually more severe with the age issue?
Simply because in this case, expanding freedom for some would in the end reduce freedom for most of us. Same with pedophilia.
If two consenting men want to marry to enjoy certain benefits (and that's what it's about, legally), I fail to see the victim. Not much would change at all, since those who'd marry are together anyway.
Nor do I see society getting more unfree as opposed to polygamy (ie.polygyny for practical purposes), where society could and would change because you'd (re)introduce a new (archaic) element.
1 adult +1 adult is a good coherent model and as we can see and it seemlessly worked with gays so far in some countries.
And to satisfy your curiousity in advance, yes, if someone brings along an adult, consenting (I'd really like to see a speaking horse!) animal before the wedding altar, we might expand that law again in the future.
@Mick, do you consider anal intercourse a perversion as well? How many Tguys here do you think practice it regularly? Why did western law allow anal sex at some point? Because it got somehow less perverted?
Why is a homosexual monogamy less of a monogamy?