If your veganism is based on beliefs about humans and animals, I fully understand your doubts. You are writing a lot of truths in your post. My food is plant-based. I'm not doing it for the environment, or humans, or animals. I'm into it for myself. I know vegan food is healthier, better for me. I realize that there may be studies saying otherwise, but I can feel the positive effects of my diet. Also, years after becoming vegan, I had a serious accident from which I recovered amazingly fast. Doctors and nurses were outright stunned. When I asked doctors (that were not vegan) why I had recovered so quickly, they pointed to force of will, but almost equally to my diet. It was new to me: according to them, vegans just recover faster. That alone is enough to keep me vegan. This said, I realize veganism is not for everyone. While I appreciate great food, I'm happy eating lettuce without any salt, oil or sauce, just plain. This applies to any type of food. I'm just not difficult. Plenty of people need food they like, or even love. And yes, vegan food can be very tasty too. It's just more difficult to make it tasty. And sometimes making it tasty renders it less healthy.
In sum, I'm vegan for myself, not for anyone or anything else. And this keeps my diet fairly independent from convictions.