@Your opening rant: "Why is society supporting Lila's unhealthy path of confusion and destruction. If gender is nothing more than a social construct, why can't he be himself and remain a boy? If there is no difference, why? Heck why do we even have gendered washrooms at all for anyone if there's no difference."
Gender roles are a social construct.
Gender identity is a biological-neurological feature.
Gender expression is a conscious choice.
You can feel you gender expression is inappropriate, that certain sexual characteristics are over or under pronounced - for example, if you are male do you decide to wear a beard? (That is a part of your gender expression, and fashions have changed over the centuries, and across social classes) if you are female the biggest social arguement is over your breasts, and whether a)men should be able to dictate when they are shown, and b)whether they should be sexualised by random passerby when you are using them to feed your child? (They are primarily for sustenance, but also exist as a secondary sexual characteristic, so gender role typically set expectations on how and where they should be shown)
Nothing is 'just' a social construct.
She was not 'born male', she was assigned male at birth.
If they are allies, they have a responsibility to educate themselves regarding Trans issues. And this is a big one.
"Hmm, I'm not sure how I feel about it. I mean, since she identifies as a girl, she should be able to use the changing room for girls, but the entire point of segregated changing rooms is for women to not see someone's penis while they are changing, and vice-versa."
Is that the entire point? And if so is that justified.
First of all, i am a trans ally; i have lived with a trans woman. We have shared a bathroom. The last thing she want is for me to 'see her penis' - this is a part of her body which is associated with dysphoria, probably a lot of shame and discomfort. Most trans women don't want anyone looking at their genitals. They don't want to look at their own genitals.
If the only reason for gender segregation of looker rooms is to stop girls seeing a penis - and this leads me to ask if you want to ban all pronography, or just gender segregrate it, so only homosexual acts can be depicted and only men are allowed watch the males, while only women looks at the females... - IF this is the only reason, then i'm pretty confident that ANY trans girl is going to be hiding her penis better than you can even begin to comprehend.
I suspect that the reason for gender segregated public toilets was to prevent public sex acts. (Though obviously this doesn't prevent gay sex acts, in fact it may encourage them... ) i suspect that Victorian attitudes towards sex were at work (at least in england) and that we have inherited this.
I am also sex positive, and believe these attitudes are harmful, that they contribute to rape culture and unhealthy sex lives in general - to an unhealthy and dangerous sex industry.
Overall, there is a big issue which needs to be dealt with; and not just trans rights.
I don't know many gender fluid people, so i don't know what they think. As such i believe they should be asked the question, an i should not presume to answer for them. They are the ones most affected by any decision.
So, why are we segregating based on gender at all?