That is the crux...many think the Church's teachings about sexuality are wrong, for both straights and gays.  I'm not sure of the exact figure, but more than 50% of US Catholics don't think homosexual acts are immoral.  If there is a failing in Fr. Martin's book, it's that he doesn't call on the Church to change its teaching on homosexuality.  It's understandable.  The Church hasn't changed its flawed teaching on straight sex, let alone gay sex.  It's also true that in many countries Catholics don't accept the morality of gay sex.  A number of people like joanp have said the problem is the Church hasn't been forceful in teaching about sex, but if they were, it wouldn't be accepted.  It would be interesting to know how many religious actually believe the teachings.