You sound like what I like to call a "debatist." No one wants to be challenged on their personal choices. You don't seem to be approaching this concept with an open mind. Can you define what makes anything they say unreasonable? I am not vegan, but I can recognize, definitively, that veganism is better for the environment (by far), healthy (if you make sure you're getting all the nutrients you need, just like any diet), and less cruel to animals. You can choose to disagree that those conclusions mean you need to cut out animal products, but those aren't opinions up for debate. Farming meat is far worse for the environment, vegan diets are perfectly healthy, and obviously, killing animals isn't something the animal wants.

Again, you can disagree with their conclusion that those reasons mean you shouldn't eat animal products, but denying that they're true is like denying climate change. I'm not vegan, so clearly I didn't come to the same conclusion, but I'm not trying to purport that anyone that does is somehow unreasonable.