Your point is very naïve if you expect me to believe that an educated person (esp. a practicing Christian) is ‘invincibly ignorant’ when they reject the tenet that homosexuality is a sin AFTER
being shown from Scripture and Church teachings that it is . You may as well say that a Christian is ‘invincibly ignorant’ when they reject that Jesus really exists or none of the supernatural stuff happened. In these cases there is a point when you can tell when someone is not being reasonable.
We find in Scripture and Church history that Christians did not put up with such ignorance and unreasonable thinking. Ignorance was dealt with by setting the person straight or applying Church discipline which implies culpability. The Church seemingly had no problem burning people at the stake for heresy with seemingly little consideration of ‘ignorance’ being involved. The disciples also had no problems judging people of being false teachers (1 Corinthians 5:11-13; Galatians 2:4; 1 Timothy 1:3,4; 2 Peter 2:1-3; 1 John 4:1-3, 6; 1 Corinthians 6:1-4

and they rejected them accordingly.
As a non-believer, one of my interests here is to discuss Christianity as it is, with all of its good and bad. It is far from appealing when some Christians try to water down the bad side (the parts that go against current popular norms) just to get me to look at their religion in a better light. I’d rather come up with my own moral system, which is all that a relativistic moral system amounts to.