It's usually only a matter of minutes for someone to ask why one is vegan. Folks give a lot of reasons ranging from the antibiotic content in animal products to the environmental sustainability of a plant based diet. Those are all fine reasons to change your diet, but none compel humans to make radical changes in the ways they live their lives beyond the dinner table. You can be healthy, environmentally conscious, and hip and still consume animal products. You'll have problems making ethical arguments, however, if you do.
I am a vegan because I know that sentience is the only relevant characteristic when it comes to determining personhood and agency. Just because an animal doesn't look like me, think like me, or act like me doesn't mean I get to use it for my pleasure or convenience. This means I don't eat, wear, or use animal products or those tested on animals. Non-human animals have a beautiful, personal existence in their own right and have a continued interest in that existence without my interference. Who am I to demand they give their bodies and babies to me for even one meal, or one coat, or one day of amusement?
If you'd like to learn more about ethical reasons for becoming vegan, check out the links below. The only way we'll really change how we treat animals is if we radically change how we think about animals. Everyone takes their own path, but I hope everyone works toward being vegan; it's the LEAST we can do to do right by all species on this planet.
Boston Vegan Association
My Face Is On Fire
The Vegan RD: Thoughts On Being Vegan, A Dietician's Perspective