Humans can have more complex emotions. We can be stressed about theoretical concepts that animals just are not equipped to understand. We can be excited by the prospect of future events.
Most animal emotions are immediate. They enjoy some food they eat, they find a nice warm spot to bask in, they see a predator and run away. Most animals lack the mental capacity to think beyond the immediate.
Silly vegoon, only the cute animals I didn't want to eat have feelings. The others are unfeeling slabs of meat that is magically created by wholesome farmers being folksy.
As a new parent the agriculture propaganda from the very start is crazy! Look at this happy farmer and his cute pig its so happy in its mudpit, what a wholesome picture!
I don't eat meat, but the more we learn about plant intelligence, the less I can say with confidence that plants do not have their equivalents of things like pain and emotion. It doesn't help that we have great difficulty defining what emotion means.
But we know a lot about plants now that we thought were animal things. Grass "panics" or "screams" by sending out chemical signals when you cut it as a warning to others of its species that they are seriously injured and danger is coming. That's what the smell of fresh-cut grass is. Sure, calling it a panic or a scream is anthropomorphizing it, but it's kind of hard to describe it in other terms.
We also have learned about "mother trees," which will send resources to their offspring if the offspring let the mother tree know they are in desperate need of them. Which sounds very much like parenting in animal species. There's also lots of evidence that plants can learn from experiences and retain some sort of memory of them in some capacity.
Do I think plants have the same sort of sentience as animals and will I stop eating broccoli? Of course not. But I will still have to admit that at the end of the day, I might just be choosing to cause a different kingdom of life pain and suffering because it's far enough away from my species that I don't consider that to be pain and suffering.
If you're eating meat, then you're contributing to the death of all of those plants that had to feed the animals you're eating. Even if you grant plants sentience, veganism is still the more ethical option.
You're conflating very different processes here. While there is the hard problem of consciousness and we can't falsify ideas like panpsychism consider a few things.
If you amputate my hand and press on it it will emit nervous signals. Does anyone feel pain? If you destroy most of my brain but keep me alive, then stab me almost all the nervous activity and hormones etc associated with injury will happen. Is there any reason to believe there is any pain felt?
I would say no in both cases, pain is not emitting nervous impulses, or something that precedes releasing endorphins and inflammatory factors etc. Pain cannot even necessarily be reliably correlated with stress markers like heart rate, and in the case of phantom limb syndrome pain can even be associated with a complete lack of signals.
There are good evolutionary reasons to exhange information and resources, even unwittingly. Apparently some bacteria in my tummy are in conversation with my body constantly but I'm not at all aware or actively participating in that. Maintaing pain only really seems to offer advantage if you can do something about it, while it's possible for things to exist accidentally it's not like grass can move to places without mowers or trees shade themselves. In all animals with nervous systems the nervous systems are the vastly most expensive thing to keep alive. In fact there are a few creatures who when entering an immobile stage of life rapidly digest their own (a good explaination for both tenure and retirees!).
Plants don't have rapid long distance communication in their bodies, they don't have centralised organs, they don't even have anything approaching the levels of activity we associate with the simplest nervous systems.
It's probably best to think of grass "screaming" as skin cells "screaming" for resources to make more melanin when exposed to UV. Or lymph nodes "screaming" when releasing hormones to heal a wound and stuff. This is all vastly below the level of consciousness.
Or whatever, embrace panpsychism, like the invisible dragon in my garage nobody can prove it false /shrug. Animals eat plants though and thermo law 2 is a thing so even panpsychics minimise suffering by being plant based.
It doesn't help that we have great difficulty defining what emotion means.
There was this thing about fishing with hooks. Apparently it's ok, since fishes don't have the facilities to process pain as anything different than a robot would interpret sensory input.
Believe me vegans put a lot more thought into nutrition than omni's do. Aside from that pet ownership is not vegan. The word "ownership" being operative. If you find yourself having to care for an animal then that's a different situation of course.
Obligate carnivores in nature. Why do you care if a cat is fed with fortified plant bits vs fortified animal bits? Neither product exists in nature and the cat can live a healthy life on both. Also breeding cats to be pets is completely unnatural, so why are you fine with that?