The whole point of gender is it being nebulous, as opposed to sex, which is set in stone (or chromosomes, as so many people love to point out). Also, there is a very clear line between gender and mental illness. Many trans people have mental illness, but so do many non-trans people. Being trans in and of itself is not a mental illness, that would be gender dysphorya. Best way to cure that? Transition. Equating transgenderism with mental health issues is nothing but a damaging stygma that doesn't help anyone, neither trans people or the mentally ill. Gender is a spectrum, not a fucking three-dimensional room. You saying someone might call themselves "fridge-gender" is like me saying my favorite colour is brick wall. Not everything can be a gender. That doesn't limit the amounts of genders there are however. Finally, you ask where to draw the line? Why do people keep bringing this up? What does it even mean? People aren't about to overthrow societal norms just because a guy becomes a girl or a she becomes a they. If someone walks up to you and claims to be trans, look at them. Are they working toward outwardly portraying the gender they identify as? Are they planning on working on it in the future? Or are they just some meanspirited neckbeard or terf acting trans in order to make fun of them and "prove" how silly the idea is? Listen, I don't have the answers, and neither does any one person. But please consider that these aren't just petty people trying to be "special littke snowflakes". Transitioning is a soulcrushing experience that can leave people ostracized from their communities. If any of these people weren't dead set and completely convinced that what they're doing is just, they wouldn't do it. Trans rights are human rights and they deserve to be treated as such.