They're a loud minority, in my experience. In my time as a queer woman subreddit mod, I often had to wonder how many of these TERFs were actual women, and how many were just trolls or bots. They definitely used all the tactics of the alt-right, including brigading subs, trying to doxx users, and bullying trans women out of queer women spaces.
There are also an uncomfortably large amount of older white feminists that have transphobic views. This is likely due to the 'gender crit' style of radical feminism popularized in the 1970's. Gendercrit being that they try to set up this false dichotomy between freedom of gender expression/gender norms and gender identity. I.e. "Trans women can be fine just being a feminine gay cis man." This completely ignores the reality of queer trans women, non binary identities and trans men,, amongst other issues.