It doesn't really matter whether it's sinful really, lots of things are sinful. Working on a Sunday is sinful (Exodus 35:2), Wearing clothes of more than two types of thread is sinful (Leviticus 19:19), it's a holy commandment not to take the Lords name in vain, so if you've ever said "god dammit" that's sinful too. It's very difficult not to be sinful.
Don't forget that it is also sinful to trim your beard (Leviticus 19:27) and sell land permanently (Leviticus 25:23).
The sins of others does
not give one a reason to treat them poorly. If I were to be the devil's advocate here and say that being homosexual is a sin, there is still no justification in committing hate crimes and spewing profanities in the direction of homosexual people I meet.
I do not believe that homosexuality is a sin, nor do I believe that wearing clothing of two different kinds of threads or selling a house is a sin! People need to remember that the bible was written with the best knowledge of the time, and depicted relevant practices to the time it was written in. Have we not advanced since then?
The seclusion of homosexuals in laws or rules simply fuels hatred. Is wrath not a
deadly sin? Don't you think that saying "gay is ok" and pushing gay equality through media and other means would persuade people to drop the anti-gay mentality, and stop
worse sins such as hate crimes and violence? Anti-gay laws don't exist because the bible says it is a "sin". They exist because people
hate homosexuality. When is it okay to hate another human?
If anyone says, “I love God,” and hates his brother, he is a liar; for he who does not love his brother whom he has seen cannot love God whom he has not seen. (John 4:20)
Whoever says he is in the light and hates his brother is still in darkness. (John 2:9)
Hatred stirs up strife, but love covers all offenses. (Proverbs 10:12)