Knowing them growing up, you could tell they were different, but what they struggled with wasn’t a thing that their parents did to them.
I’m sorry but you have absolutely no intimate knowledge to be able to discern what you proclaim. The influence of our parents on us, is for all of us, a complex phenomenon, one which does not become apparent in the short term, necessarily, and which we tend to work out – positively, negatively,and neutrally – over time in our own childhood and adulthood. In fact, we are affected by all of our relationships, but no more true is that than the intimate relationships (including with siblings) within our birth family, with “issues” being replayed and worked out, for some people, until death. This is the primary and primordial “laboratory” which forms our self-concept.
Very often we are unaware of how our behavior is a reaction to (again, positively or negatively) our parents’ behavior with/toward us. Much of our self-concept is formed from unconscious dynamics between our parents and ourselves, so for you or for me to say “my parents had/have no effect on my sexuality” is not a reliable statement. Nor is the effect on that sexuality, of which psychologists speak, necessarily an overt and direct one – such as comments on a child’s masculinity/femininity, etc.
Truly unconditional love is rare in parenting. The exceptionally secure parent and exceptionally virtuous parent is able to provide that, but it is far more typical to register covert & indirect disapproval of a child who in some sense is "different’ (no matter in what way different) and/or a “disappointment.” Most of the time, our imperfect parenting will not, thankfully, have a disastrous result, nor will it necessarily result in a homosexual lifestyle. However, with enough original biological impetus for an individual, combined with encouraging influences from other individuals (or from society), combined with absent parenting, disconnected parenting, or ambivalent parenting, a perfect storm is unsurprising.
It’s not a question of what parents “did” “to” a person – your friend or my friends. It’s more often what was not done “to,” and especially “for.” Neither someone from the outside, nor even the individual in question, is necessarily in the best (short-term) position to make an objective judgment about that. It takes the individual honestly examining his entire pattern of response to family dynamics, in a professional setting, to determine that with the help of a professional.
It’s extremely logical that those who may have an inclination for SSA might end up with an intimate partner who accepts him or her fully, and that such a compensation for previous inadequate validation of his or her integrity restores that self-image which he needed most in his early, primary formation of an identity.
Btw, personally I know lots of homosexuals, some of them for many, many years, and some of them in my own family.