The author points out how arguing with meat eaters usually accomplishes little but to feed whatever they're feeling defensive about.
I've gotten trapped in this many times before. I've learn that eating meat or driving cars has environmental costs that I do not want to be responsible for. Being me, I compulsively collect research on these things and can speak for hours on all the knowledge supporting my decision.
When I argue with someone about this eventually the argument breaks down into either them feeling guilty and resentful or insecure and resentful. And eventually I notice that I've put even more stress on the relationship. Realizing the futility of arguing I am silent for some time until the frustration at seeing so much that to me is obviously wrong boils up and I have try arguing again.
The author explains why this is so vastly unproductive both just offending everyone and preventing anyone from actually changing, she also provides suggestions for alternative behaviors that are less likely to trigger defensiveness.
I also think the activist should read this book too. She's also really passionate about her beliefs and is still trying to guilt people into changing. (Which rarely does anything but make everyone resentful).
Though for me it's challenging to teach through example when you believe that it's imperative to humanity's survival for as many people as possible to change.
To everyone I've ever harassed for eating meat or driving, I have a greater appreciation how since even my actions can make you feel judged, when I also start explicitly judging you, I must be nearly intolerable. I'm sorry, I will try to be more sensitive in the future.