Hi Cain. I think there are at least two factors here.
1. One is people go through their "grief phases" and project anger onto one political and religious issue or another, outside of themselves. This happens with any number of issues. It is not specific to animal rights.
Of course, there is some personal projection of their own internal conflicts with learned helplessness. Some of these people act like teenagers in angry rebellion, still fighting between authority figures and taking responsibility for managing their own business. They see problems, but feel powerless, so they blame on others.
This anger phase will pass, but like having teenagers in the house, it's a FU pain.
2. As for animals rights specifically:
For each person who puts humans first, and trash animals and environment as expendable, there are people who worship the earth and animals in place of God, and denigrate humans as worthless selfish parasites blamed for the abuses.
Some who go to opposite extremes even blame religion for destroying earth by teaching material life is sin and the only heaven is after earth is passed away etc.
Truly peaceful animal/earth lovers also love and respect people EQUALLY as part of the same equation. They don't get religious about it, while blaming religions!
The truth is somewhere in between: yes, people have greater responsibility, but yes we need to restore balance to the planet not just between people but plants and animals as well since the ecosystems involves keeping all these in harmony.