I promise to try to answer this question in a way that's not preachy. However, I *am* vegan, so filter my post in whatever way suits you.
On that note, there's another couple things that's always bugged me. Why do some vegetarians eat fish and/or chicken but not duck or lamb, and I'm not talking about the dietary-consideration kind? And why do some (ie. vegans) go as far as to not eat animal products like eggs, milk and the like, including from "ethical" sources? Because I have never had a rational, coherent argument with a vegan. I'm pretty close to just dumping them in the "ewww intestines" category.
While I can't speak for all vegans, the general consensus is that we don't eat byproducts (milk, eggs, honey, etc) from humanely raised animals because it's not freely given. It's still unnecessary exploitation, in our opinion. This is why breastmilk is vegan (it is freely given), but cow's milk is not. I'm quite happy that you didn't come out with the "cows would be in pain if we didn't milk them" argument. I get that one a lot, from people who haven't done much research on biology (this wasn't a dig, I promise).
As for your other points, I'll touch on a couple of them, if you don't mind.
Reason 3: It's unethical to cause suffering. Thus it is unethical to eat meat.
Now we're getting somewhere! So if in the future we hooked up newly born cows to a Virtual Reality system ala. the matrix, where there was no suffering, disconnected cows would remain virtually in the world (no percieved death or loss) and execution was done painlessly and with the cow blissfuly unaware, it'd be okay to eat meat? Somehow I don't think a real vegan's going to say yes. So what's the real reason?
Er... no. Again, in my own personal opinion, it's about reducing exploitation. Would it be ethical to do this to people? Most people would claim that it is not. When one asks why it's okay to kill an animal but not a person, one often gets the answer that humans are smarter. Yet, when you ask if they would treat a mentally retarded person as an animal, it seems to be out of the question.
In general, my stance is that we should grant, to as many beings as *practical,* the "rights" of life and self-ownership. I don't want rabbits to be able to vote, because they're not capable (so far as we know) of agreeing to societal contracts. However, we generally afford those basic rights to anyone.
Frankly, the decision to grant the rights of life and self-ownership to humans only seems a bit arbitrary. At one point there was certainly a practical aspect to this, but I doubt many people (at least in the USA where I am, and many other parts of the world) would be able to claim much hardship if they gave up animal products.
Reason 4: It's unethical to kill.
What, now plants aren't life?
Reason 5: Plants aren't on the same level as human beings.
Then why are cows? Rabbits? Sheep? Birds? Insects? Where is this magical, arbitrary line that says it's okay to eat a pumpkin but not to eat a fish?
Again, the objective is "as much as is practical." It's fairly easy to live without eating animals, or their byproducts. As far as I know, it's not at all practical to live without eating plants.
As for the ethics of killing plants: If you're really concerned about it, the best way you could reduce the killing of plants is to stop eating animals. The energy conversion rates are astoundingly bad. Look it up if you don't believe me.
Reason 6: Meat is bad for you.
Citation needed. Last I heard you need a meticulous diet of a huge array of vegetables (something that no human could have done pre-civilisation) to maintain a healthy vegan life. We've been eating meat since the dawn of man, literally, and yet here we are living just as long as the average vegetarian. However, this is the only reason on the list I could accept as being non-retarded. If you honestly think you feel better on a vegetarian diet then hey, don't let me put you down.
Any diet needs a huge variety to be healthy. If you're interested in the health aspects of veganism, I'd suggest "The China Study." Make sure you look up the refutations as well, as I found some of them to be valid concerns. Even so, presented was a fairly large amount of evidence (in the form of correlation), that a vegetarian diet is generally healthier. It's hard to find sources that are "unbiased," since this is a charged issue and there seem to be few impartial researchers that I've found. The best I've been able to do is find sources that seem (to the best of my limited knowledge), logically consistent.
Besides, tradition is not really considered a great option to keep doing something, right? We'd still have slavery and human sacrifice, as well as a whole host of other problems if we let tradition dictate our lives. Please note that I'm not in favor of abandoning all traditional values; I just think that from time to time we need to reevaluate our reasons for doing things.
As a side-note, if you care, I've only been vegan for a few years. Even so, when I look back at the reasons I had for being a meat-eater, my reasons look a bit weak. I think it mostly boiled down to: "I wanted to eat meat." Frankly, most discussions I have with people on the subject eventually devolve into either this, or the "faith" argument. At that point, you can no longer rely on logic, and further discussion is pointless.
Right then. Sorry for being long-winded. I hope this answers some of your questions on why vegans (or, at least, this particular vegan) acts the way he does. Habit really does shape belief, right?
