Pronouns are not based on biology.

Pronouns are supposed to be an indicator of someone's sex, not someone's made up sense of gender identity. Sex is strictly defined by the gametes your body was designed to produce, regardless whether your body is actually capable of producing them. Sex cannot be changed no matter what you call yourself, what hormones you take or how many plastic surgeries you have.

I am a cis woman and I am secure in my own identity. Yet when people use "she" for me they are validating my identity. Why is different about trans people?

We use "she" because you are biologically female, not to validate your identity. If you decided to call yourself a man, take hormones and insist other people use he for you we would still use she.

Even if you don't believe in this language you can still return the same respect that Buck gives to you. I don't know if Buck can be considered GC but he holds GC beliefs.

So, just because Buck is nice to us means we are morally obligated to change how we speak?

Buck is a man. He has a beard, deep voice and male levels of testosterone.

Buck is a woman and will always be a woman.

Using preferred pronouns is absolutely a neutral and respectful act. Most major news and information sources use preferred pronouns, and if they didn't TRAs would boycott them. If TRAs were such a tiny minority of people, we wouldn't have this much influence.

No. Saying "he" for a woman is absolutely lying. When I say "women" I am referring to all AFAB adults, regardless how they identify. Just like "man" refers to all AMAB adults as I don't believe in gender identity or that sex can be changed. Like you said TRAs bully people who dare to question the trans narrative. It doesn’t mean most people agree with them, it means TRAs are effective at silencing people.