I would agree that the conditions for 'animal farms' are pretty atrocious across the board including the living conditions of the animals, the generated waste, and all of the antibiotics/hormones used in their production. A plant based diet produces less waste, but there are some concerns with larger scale agricultural production such as fertilizer use. I have several friends who are vegan and/or vegetarian and I admire their dedication. However I have some arguments against veganism and the points you made.
1. Scientific research/safety is dependent on testing the effects of drugs, chemicals etc. on animals in order to determine effectiveness, toxicity and lethal doses. Obviously these animals are suffering but it is for the purpose of furthering our scientific understanding and preventing human suffering. Is this worthwhile?
2. Humans are what we are today because of diets consisting of meat. It was not until the development of modern day agriculture and transportation that a vegan diet became possible. Many early civilizations were hunter and gatherer base societies which allowed for population growth and movement as meat is more calorie dense. There are some evolutionary traits that point to an omnivore diet. Humans don't have multiple stomachs or bacteria that can break down cellulose like cows or gorillas do. As for the point about teeth, canines in herbivores can be used for other purposes such as defense, mating, and breaking up plant matter. Human evolutionary brain development could also be very well linked to the omnivore diet our early ancestors relied on.
3. I might not be are but to my knowledge there are no comprehensive/long term studies that argue that a vegan diet is any better than an omnivore diet. I know vegans require a vitamin B12 supplement and need to eat certain foods to obtain essential amino acids. Could a switch to a strictly plant based diet have other long term and/or developmental effects that we are not aware of? Maybe, maybe not. On the flip-side the meat we eat today is genetically modified and treated with antibiotics which could be just as detrimental as our early ancestors were dependent on wild game which are much different from modern day farm animals.
4. Speciesm is a weak argument in my opinion. As humans we make collective decisions within society to decide what is moral and immoral. I can only laugh at the idea of the declaration of independence stating "All species are created equal". Dogs and cats are valued in society whereas pests like cockroaches, termites, and mosquitoes we exterminate if we find them in our homes. If our dog has a tick we remove it. Should we bring all natural carnivores to trial for their serial killer like tendencies?
Does the fly Obama brutally executed on national TV not have feelings and a family? First drone strikes now this?!?! Has the power of the president gone too far?!?! /s
Sure the way animals in industrial meat production have little quality of life, but the idea that all animals should and can be treated equally is preposterous. There is a natural hierarchy in the food chain.
Just presenting some counterpoints and playing devil's advocate.
I would recommend anyone reading The Omnivore's Dilemma, a book that dives into the modern day food industry. It does not advocate for veganism but talks about the industrialization of food including meat and produce.