First, actions speak louder than words. The church talks a good game, but it doesn't have the best track record among gays, blacks and women.
Second, Mr. Christofferson mentions that a segment of the population that leaves the church does so because they don't feel accepted or welcome in the church. I am sure such people do exist, but in my experience, feelings of alienation come as a result of deeper issues and doubts--not because Mormons aren't "friendly" enough. John Dehlin has studied this and his work shows that "being offended" or "not having a friend" in church are among the least common reasons people leave Mormonism.
Third, the idea that Mormons welcome diversity is tenuous and conditional. What they really mean is that they welcome all to adopt their culture and religion. This is demonstrated by their massive missionary efforts, through which they send tens of thousands of young adults (most of whom are straight out of high school) with the sole purpose of convincing everyone on earth that their world view is incomplete and flawed and that Mormonism is infinitely better. A large part of culture is derived from the predominant religions in the region. Which means that even though some people who have joined Mormonism have been able to assimilate some aspects of their culture (i.e. Polynesians), the roots of their culture of origin must be gutted and abandoned before they can truly accept Mormonism ("Thou shalt have no other gods before me").
When I hear Mormon leaders talk about diversity, what I really hear is a fleeting hope that enough non-white people will join the church so that they can be taken seriously as a major world religion. An ambitious task for a religion boasting less than 1% of the global population.