Whoa, Whoa! WHOA!! What??

Another of those impromptu conversations on the beach turned up a disturbing idea: Have pro-male activists been targetted and murdered?

Thinking about it, it's very possible.
These men and women are talking about changing national policy affecting billiions of dollars in funding, in an emotionally-charged area of the law. The established officers of the courts, police, and other legal agencies are using prejudice and fear to control that spending and put it into selected pockets.

In the US during the Civil Rights' Movement, a busload of people from a 'Get out the vote' drive were killed and the entire bus buried.

My own times

I know when my ex threatened to have her sons or her former brother-in-law come beat me up, I took it seriously. Most of those threats came when I was barely able to walk. After I got better, I rationalized that my fears were based on my own sense of feeling vulnerable and crippled.
When her older son was discovered to have had a brain tumor, at first I breathed a sigh of relief. He was her main conspirator in the extortion plot. Then I realized that the real danger probably came from the younger son or daughter. Neither of them proved to know any sense of right or wrong other than what their controlling mother told them.

What happened after she filed spurious Intervention Orders certainly convinced me it could happen. For months after the second trial, they would drive past the house where I rented a room, yelling and making lewd gestures. The neighbors told me to call the police. My new landlord was frightened.
I have to admit I walked very carefully when I went outside.
I even had nightmares of her daughter or younger son walking up and shooting me full in the chest. They'd shown me unregistered guns. I'd wake up dreaming that I felt the tug of the bullet and saw the hole.
I gave them what they wanted -- an inequitable settlement -- with the proviso that I didn't have to see any of them again. They seem happy enough with their successful extortion. Other than a few drive-bys and gestures, I haven't seen any of them.
If these folks want to go to such lengths not to talk to me, that's fine.

Have there been politically-motivated killings?

Considering the corruption of the legal system in Victoria seems to be nearly complete from top to bottom, I don't imagine an attack on a Family Rights activist would even be investigated. It would be easy enough to cover up the reasons for a killing.
In the current atmosphere, even a cold-blooded murder could be blamed on the man. It's already happened.