The LDS Church is obsessed with sexual purity, teaching that "sexual sin," defined as the "illicit sexual relations of men and women," is the worst sin of all, next to murder. That includes any sex outside marriage between a man and a woman: adultery, fornication, and (of course) any sexual activity between people of the same sex.
It's almost kind of refreshing to see boys wearing shirts like that, because Morman purity culture is so often laser focused on women and girls. That kind of preoccupation with policing people's personal lives is, of course, not healthy for anyone, but Mormon girls as young as 12 are particular targets, being frequently admonished to dress modestly, lest showing "too much skin" (whatever that means) should tempt males to sin. 
Mormon kids who are LGBTQ+ get the worst of it, because their religion strictly forbids both sex outside of marriage and marriage between people of the same sex. They are left to choose between leaving the faith they were rraised in or living a life of celibacy. 
I'm sorry if I sound like I'm dunking on Mormons. I'm not opposed to the LDS Church or its followers, per se. What I'm opposed to is the kind of strict and punitive purity culture that causes kids to feel guilty about every sexual urge they may feel and/or arouse in anyone else, and the purity culture of the LDS Church is particularly strict and punitive in that respect, from what I know. In my opinion, kids who are raised in a culture like that are more to be pitied than derided as "stupid and pathetic." They've been brainwashed since childhood. That is NOT their fault.
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