It's not just animal products. They're against the use of animals "against their will". Since most animals don't have a will vegans just assume they don't want to do stuff for humans and so are against consumption of anything that uses ("abuses") animals in their production. So no milk because it abuses cows, no medicine that was tested on rats, no horseback riding (I guess?), etc.
They are doing a "favour" to the animals they indirectly save by reducing consumption. Plus they're idealists, hoping that the entire human world will eventually stop using animals. Most of them probably know the impact they make isn't too big worldwide.
So, back on the questions
- "Not wanting to" do something is only applicable to complex enough animals. If it's moral to kill to eat depends on how much "suffering" is the animal capable of feeling (and how much it suffers while being killed), and maybe how much food do you get per kill. Any rule you choose will in the end be arbitrary but it's good to at least be consistent with it.
- Honor is useless to your dead ancestors so... Some people may actually think something similar to this, but it's quite a stupid argument to make IMO.
- Don't care much. If you see everyone as a resource and treat them well anyways you'd be a better person than someone treating everyone like crap.
