@oginohusband There's a lot to unpack here so lets get to it...
Japan is pretty regressive when it comes to lgbt rights, but it's not all taboo and it really depends on what area you;re in and what your family/community is like.
Nobody's sexuality is "wrong". It's not something you just choose. (don't confuse suppressing your sexuality with "choosing") Everyone has every right to be exactly what they want to be and only absolutely horrible parents would discipline or disown them for that.
Being gay is not a mental illness. It's portrayed as normal because it is. Opponents of lgbt rights usually fear the "normalization" of it the most because they use dehumanization or "mental illness" tactics to oppress others. If anything, creating a society where being gay is stigmatized is the inhumane and immoral one.