The received theological wisdom is that the bit in Romans they cited means 'don't have an orgy' and not 'homosexuality is wrong'.
Even if this wisdom is incorrect, it's certainly the case that Jesus never said anything on the topic.
Well, no, it isn't the received theological wisdom. Even among people who aren't evangelicals. There are some people who think that, which is a different thing all together.
The idea that what Jesus said is valid and anything else isn't, or even that only what is explicitly stated is important, is also not the received wisdom.
Christian teachings on sexuality are part of a larger set of beliefs around the purpose of sex, and even the body in general. Historically they are quite strict, for everyone, ideally people are only meant to have sex if they are willing that a pregnancy could result, only with one spouse, and no sex during times like fast days, lent, and so on. Celibacy being the rule for anyone who, for whatever reason, doesn't marry, being the expectation.
Not to say that people have ever been very good at all that, but it's a coherent perspective that fits together with a lot of different teachings about the body rooted in both the Bible and also the philosophical tradition Christianity comes out of.
Evangelicals can have an odd tendency to pick and choose from that, but it's just not accurate to say that the real theological understanding is what you'd expect to hear from some of the Jesus seminar type people.