Why are those who are knowledgeable in certain subjects shunned by some in the community?

We had a veteran who had valuable information to share regarding mental health yet he was shunned by a few so badly that he deleted his account. I witnessed it. It was awful.

I’ve been shunned because I’m a transgender ally and I have helpful information to share.

Are some of us shunned because we are vocal about taboo subjects?

The medic isn’t shunned.
The pet advocate isn’t shunned.
The MacGyver isn’t shunned.

?