"Love is love" and "love is enough" arguments don’t work, as marriage is not just about love. Marriage has multi-faceted features like anthropological, biological, and social aspects intrinsically tied to itself.
gender and sexuality
If the person in question claims and strives to be a Christian disciple, a Christ follower, then the issue without attempting any semantic gymnastics is plainly - sexual sin! More importantly, if the person in question is not a Christian yet - the primary issue then is - salvation!
Another crucial piece in this discourse that we so often tend to ignore is that we all are part of this fallen world! We are all fallen people. We all are sexually broken! We are all on the same large broken boat, perhaps on different decks. So all of us primarily need the Saviour!
To understand we ought to know. Oftentimes, we don’t know the ABC of LGBT but have arrived at conclusions and are busy giving recommendations. There is a huge knowledge gap that we could be guilty of if we haven’t done the first thing in learning about this issue.
Along with the eunuchs (asexual), the inter-sexed are the only population that could say “I’m born this way.”
For the 'sexually disadvantaged' (asexual) the Scriptures have comfort and justice.