Their biggest line of defense is "animals are alive and they have feelings and senses, we abuse them for food". That's sadly right. And they implicitly say that "eating plants are OK because, plants are not animals and they're just happen to grow. They don't feel, they don't understand".
On the contrary, there's a growing mountain of research revealing that plants can communicate, issue warnings about diseases and bug infestations. They so-called get stressed when it rains, and their metabolisms startle during fast light changes (like eclipses). More shockingly, they release all the nutrients they store when they sense they're going to die, so other plants can thrive from their remains and nutrient stocks (writing this really moves me).
This is complete opposite of "plants are well, just alive wood" hypothesis. When I share this research with vegans and vegetarians, their response is: crickets.
Moreover, most hardcore ones suggest that we don't ever need meat to thrive or live a healthy life however, we've evolved that far because we consumed meat. Meat made us and, same people are ignorant of this fact.
I can understand that we need to grow these animals more ethically. This is why I always try to buy ethically produced food. I understand that these animals are adding great amounts of greenhouse gases. I can understand that we may live well with less meat. However, we need to understand, some of these animals are evolved under our reign and they may not survive outside farms for long. The cattle are grass puppies now and are essentially "useful pets". We need to understand where we are to move forward. Ignorance and fight won't take us anywhere. We need to talk openly and need to put our prejudice aside. We need to learn and understand first.