@ElleWoods15 Elle, could you reply to Flirts' post a few scrolls above? I think there's definitely a point in responding to her attempt to understand where you're coming from.
The issue is that we're finding it hard to apply your application of "(in)valid" to a scientifically proven, verifiable fact. To us, it's like someone who believes the earth is flat saying that the scientific consensus that it's a globe isn't "valid".
I had a conversation with a teen last year who believed that all views were equally valid, to the extent that she wouldn't even accept my argument that she'd, surely, rather receive a doctor's informed diagnosis than my own or a friend's advice on a hypothetical health issue.
I'm sure you're not taking things to this extreme, but rather that you rationalise your opinion in one of the ways Flirts suggests. Or, perhaps, you believe that a "sex change" operation really does change an individual's sex. (I'd counter this by saying that it may change some secondary sexual characteristics, but little else and not the fundamentals of gametes, chromosomes, skeletal structure etc.) My other thought is that you may be saying you believe sex lies on a spectrum. (My response to this would be that there are, as ever, outliers and a tiny, tiny minority of individuals who may be difficult to classify without debate about what we understand by sex, but for the vast, vast majority of the species, sex is about as consistent a binary as it's possible to get in the natural world (- a popular, if somewhat clumsy and insensitive analogy: some humans may lack a limb, but humans are still bipedal).
Another thread at the moment asks why threads such as this collapse into "bun fights". I wouldn't honestly say they do - as a poster there points out, there's actually a lot of respectful, considered discussion on almost all. However, I've resisting adding to that thread (so far!) that one of the things I do think can lead to frustration and more dismissive or rude posts (and I think there are some from both sides on that very thread) is a resistance to engage or explain one's views with the justification that others' views are too unreasonable to challenge. This, to me, just doesn't hold up as a valid (hah - sorry!) argument. Seeing this is one of the things that has led me to be GC.