One thing about being a vegan is that you may improve the compassion towards animals yet be an angry person. Sounds a little paradoxical. But yes, there are some angry vegans, including myself. Hey! We are suppose to help contribute to a more peaceful world by reducing the hate in the world with less killing of animals, but now we are adding on to it instead. Why did it turn out this way?
Why are we angry? Angry because the world continues to use animals without end, people trying to put you down because of your diet, people who treat animals cruelly, people who simply shrug their shoulders and chomp into their burgers even when informed about vegetarian benefits... we can even be angry with people who try to encourage us to eat meat out of concern of our health.
So we make justifications to prove our point to let them understand, sometimes to the point that people start to find us judgmental, condescending, inflexible, preachy and hold an all-knowing and "I am morally superior" attitude. It could be that sometimes they are right about us, but sometimes, they aren't. In both situations, no way they are going to go veg if they see us that way.
Some people put this angry energy into action - through certain forms of activism, it could be legal, it could be illegal. But hate is not going to go far even though it may seem to help at first. Eventually even supporters become tired and angry, and they just want some peace.
There are ways to work on this, to transform that anger and yet continue to do activism / promote veganism. One thing I've learned is not to hold any expectations or insist that things or people HAVE to be in a certain manner. Don't hold on to the "Vegan is right, meat is wrong" mindset so tightly. Even though we believe veganism is the ideal way of living, others may not. And we can't change them, only they can change themselves. If we cling to this mindset too tightly, we become very tense. Then just a single remark that seems to put veganism as not so ideal or someone who doesn't fall into this ideal will be the breaking point.
Let it go, let it be. Let nature takes its course. When the time is right, they will give up animal products on their own accord. Meanwhile we do what we can to "promote our medicine" by being a living example, doing activism, etc. and share with people when they want to know more.