The "we got to the top of the food chain argument" is pretty stupid, it's just appealing to nature. What "separates" us if you will as humans is our intelligence and how we pride ourselves in having morals, ethics, etc. (we call people who don't have these animals or barbaric). That's why we don't find things like rape, or even animal cruelty, etc. wrong and we as humans don't accept that shit generally.

Now consider that you live in a first world country in 2017. It is very easy to switch to a vegan diet and have a healthy, balanced diet that will be healthy and if done properly, healthier than the traditional western diet (assuming you do the proper research and know basic food science, basically im just saying dont eat broccoli all day, that's not a proper balanced vegan diet.)

If you consider that, then basically by eating meat you are killing animals for no reason, other than: you're used to eating meat so you don't want to change and to some extent taste (although those aren't really valid arguments). So you are literally causing harm to animals for no reason. When you consider how shitty the conditions in which these animals are raised (industrial farming etc). That's essentially why the ethical argument for veganism is so hard to argue, because you're literally killing animals for no reason... I find it very hard to argue against that, destiny tried but basically failed. I've always been of the opinion personally that I don't mind killing an animal personally, but I don't support the industrial slaughterhouses, where they live in very small spaces and basically live awful lives and then are killed. Like, I wouldn't mind if they lived a nice life in the wild and then are killed, but anyways I digress

there is also the health argument which is another bonus in favor of veganism: https://www.ncbi.nlm.nih.gov/pubmed/19562864

and as you mentioned the environmental reasons.

wrote way too much, oh well