A person's sexual orientation is innate - plain and simple. If you don't believe that, ask lesbians and gay men. (I have and am well satisfied with their responses.) 
Why would someone choose to subject him/herself to nonstop, venal bullying and discrimination?
As for transgenders - ask qualified psychologists about that.
We can - and should - have discussions about who can go into which bathroom. No one group should dictate to the other.
But science is valid - and those who deny it are putting our planet at substantial risk.