What's the issue with veganism?

I recently transitioned from being a vegetarian to being a vegan and it has brought so much happiness and positivity to my life. I only talk about my veganism in context or if someone else brings it up but even than I only ever get angry, negative, or just plain rude responses, nothing like the responses I would get when I was a vegetarian. I genuinely don't understand why people get so offended by my dietary choices.