I disagree with this - and here is why.
The origin of all love, including sexual love, is the interpersonal love of the Holy Trinity. Love at its best models the Trinity as a reciprocal, self-giving relationship.
Luther defined sin as being curved in on the self. Sin destroys loving relationships. In fact, one of the best ways to determine the sinfulness of a given action is to determine whether it destroys love.
A relationship is truly loving when it is reciprocal, self-giving, focused on the other. A relationship is not loving when it is focused on the self and selfish desires.
Everyone agrees that heterosexual desire is capable of leading to genuinely loving relationships. It is also capable of leading to destructive relationships. In fact, heterosexual desire is a neutral fact of nature. It is the actions arising out of heterosexual desire that are either loving or sinful.
Let's look at a couple of manifestations of heterosexual desire that everyone agrees are sinful, that is, destructive of love. Promiscuity does not lead to genuinely loving relationships because
- it is concerned with fulfilling selfish desires rather than the desires of others
- it actually harms others by intentionally ignoring their desires, e.g., the desire for a committed relationship
- it is incapable of the mutual consent that is a foundational requirement in modern sexual relationships, i.e., it lacks real reciprocity
- it may in fact be a desire rooted less in sexual desire and more in the lust for power, i.e., again, it lacks real reciprocity
Homosexual desire, according to the traditionalists, is the same sort of thing. According to God's plan, homosexuals are really heterosexuals but because of sin their sexual desire is so defective that they actually desire someone of the same sex. They perceive this to be natural but it actually is not.
Let's apply the loving relationships test to homosexual desire. Does homosexual desire lead to relationships destructive of love? In some cases it obviously can. But it is also clear that it also leads to genuinely loving relationships. It seems indisputable that there are large numbers of fully committed, perfectly normal, genuinely loving homosexual couples.
So is homosexual desire like the desire for promiscuity which always and everywhere destroys genuine love? It does not appear to be. Homosexual desire appears to be more like heterosexual desire - a morally neutral fact of nature. Again, sin arises out of what a person does with that desire.