ok here's my perspective for ya
firstly- that passage in romans in actually addressing jews. i know the book is 'to the romans' but if you follow paul's argument through he backs up the passage you quoted with "so who are you to judge the gentiles. you have god's law and you still disobey it...why don't you listen to your own preaching?" (paraphrased)
why i point that out is important. paul was trying to get the self righteous people who thought they were really moral and pleasing to god to realise that they are just like the 'homosexual pagans' that they condemn....everyone needs god's love and forgiveness and is crap at obeying god's rules.
so anyway- pauls argument in the passage quoted-
its not just refering to romans but to the state all mankind-
he says that God's existence and goodness is obvious but humans didn't want to serve god- they wanted to be god- which amounts to self worship.
that happened in the 'fall and happens in each persons life... not just 'gays or pagans'.
so anyway- that was the foundation of the sin- and then paul outlines the results of that....we worship what our hands have made...(idols of animals...our own created gods)...we worship our own bodies and place our personal desires above all else (the foundation of any sexual perversion- homosexual or otherwise)
if you read it carefully and you could study the greek if your keen...
you will see that god doesn't turn them gay...
he gives them what they wanted... he lets them deny his diety and he lets them have sex with whoever they want. he doesn't stop them. he gives them over to their passions. like a father who lets his adolescent son choose his own path in life even though he can see it is unhealthy and damaging and is going to cause his son pain...he must let his son make his own choices.
so- your question- is paul's theory about what causes homosexual desires valid today?
yeah. we are self centered creatures, all wanting to be the best. this causes all sorts of problems in the world. it causes people to be wounded by others. it causes people to desire do things that aren't what they were designed for.