Our culture has evolved over thousands of years. There is a reason things are the way they are, and you don't get to start throwing away well established cultural norms just for the sake of change.
You seem to have the idea that evolution represents a forward march of progress, but that it should have stopped thirty years ago (when you were last comfortable with it). These ideas seem to conflict with each other.
Because forums are for discussions and conversations. People can communicate ideas and get responses. Millennial's use of social media is solely about inflating their egos. They use things like Instagram and Twitter where they sprout their useless opinions, never once listening to anyone but themselves. Ever seen a group of Millennials at the mall? They're all on their damned phones, taking pictures and posting them to social media, barely interacting with each other. Older generations use Facebook to communicate, Millennials use it to keep everyone updated about their meaningless lives, never once listening to anyone else. It's all about them, their selfies, and generating "likes."
Every generation that has experienced new media forms has complained about them, and the new cultural norms that have resulted from their use. I don't know what you think you're adding to anyone's life by being upset about this.
This is not a new issue; this is not a Millenial invention.
Weird how this has never come up before in my life until Millennials started getting involved in politics. Try asking if a man should be allowed in the lady's room twenty years ago and no one would understand why the hell you'd even ask that question.
Human biology does not necessitate having different facilities for different genders' waste elimination. Almost all households don't bother with it. That they exist in public is purely a social phenomenon. We had separate facilities for blacks, too, at one point. There are biological differences between the sexes, but those don't necessarily correlate strongly to gender identity. Biology doesn't have the neat divide between these things that you imagine there is. One hopes that eventually humans will stop confusing pooping with having anything to do with either sex or gender. (It will still be polite to leave the seat down).
Myself, I have a measure of compassion for the poor bastard who has to make a Sophie's choice whenever they want to take a shit in public. I wish I could convey to you the terror and shame that this situation involves for differently gendered people.
You have to consider that there is no cure for "feeling like a woman". In all sincerity, it's wonderful that you've never felt like you had the wrong body. Having your brain tell you that your body is wrong in some way is a continual torment. Faced with the options of self-mutilation and a lifetime of social consequences, or a lifetime of body dysphoria, many people choose death.
It is easier and cheaper not to cater to the physically handicapped. Yet we build ramps and elevators, we put braille on signs, we allow service animals practically everywhere, and we accept that it is reasonable for these accommodations to be made -- that people with disabilities have a right to the same quality of life as anyone else. In this case the only accommodation being asked is being able to use a public bathroom in peace, although it would be great if we could work on not publicly humiliating these people as well. If our society is getting to the point of having to discuss transgender rights, that can only be a good thing.
There is one piece of good news for you: no one is seeking to abolish your freedom to be a bigot. What you're noticing is simply that most people are not sufficiently misanthropic to perpetuate your views.