Actually, the Mormon world has been rocked with LGBTQ issues lately, Mormons aren't all that insular in my experience, and it's quite likely that the audience members who walked out were fully aware David was gay before he mentioned it that night.
I think there's probably more going on here than what is apparent on the surface. A very senior Mormon leader made an inflammatory speech at BYU a couple summers ago in which he used metaphors of guns, violence, and war while naming and shaming a BYU student who had come out as gay (with faculty approval) in his valedictory address. (That student, by the way, is about as Care Bear unobjectionable as David is.)
That leader claimed the student's public coming out was selfish and that Mormons should fight people who behave in that sort of "selfish" manner. The leader repeatedly referenced guns and war while discussing that student.
The leader's remarks were controversial, received with approval and thanks from conservative Mormons, but condemned as unloving and unchristian by many other Mormons. The Salt Lake City Tribune featured columnists writing about it from all sides for weeks.
The LDS church is struggling with LGBTQ issues today, because large percentages of younger Mormons are rejecting homophobia and transphobia, not to mention stigmatizing and bullying behavior like that leader engaged in.
The long-term outlook for the Church looks pretty good in terms of trending toward becoming more accepting.
Just as an example ... Not so long ago, I interviewed a Mormon family in Sandy, Utah after their 18-year-old son was violently assaulted for being gay. I expected the usual sort of, "well we live in a Mormon neighborhood so homophobia is just expected here." But the real story was much more complicated, with the families' allies being primarily their Mormon community, who did not view the boy negatively because he was gay.
That's not uniform in the Mormon world, but it's becoming more common.
In the meantime, lots of more conservative, homophobic Mormons are very very very angry that acceptance is growing.
I believe that's why they walked out of David's concert. They knew he was gay, but they draw a line in the sand over public acknowledgment ... just like that leader at BYU in his violent speech.
