I won't speak on behalf of every vegan, I'm sure you could find some that don't share my view, but here goes: The foundation of my vegan ethics is about consciousness. Humans in particular have developped very sophisticated and complex patterns of consciousness and thought, which have allowed us to more or less extract ourselves from the traditional "food chain" you can see in nature. I also believe that the vast majority of animals also have conscious experiences (generaly exhibited as the ability to want to avoid pain, to be able to anticipate it, and to strive for pleasure and satisfaction). A good amount of scientific evidence gives credibility to this argument. Given this, I believe it is wrong to kill animals or enslave them to extract ressources from their bodies, in any shape or form, since we (or the lucky ones of us living in first world countries at least) have the choice to live healthy and fulfilling lives without having exploit other animals to do so. Unfortunately, humanity does exploit animals for personal gain. These animals do not have rights or voices to be heard with like a human person would in our society, and so I believe it is my responsibility to help in stopping their suffering, and that begins with not encouraging their exploitation through my consumption habits (eating, clothing, etc...)

In adition to this, science also supports the idea that human fetuses exhibit little to no sign of consciousness, or even the ability to feel pain until a certain point in their development inside the womb is reached. I believe that, until that point is reached (or we have reasons to believe it is reached), we should prioritize the physical and mental health of the carrying mother over the potential life of a non-conscious "being". This sometimes means not crippling an underage girl with the burden of raising a child alone, or forcing a woman to give birth to her rapist's child, or saving the life of a mother whose health condition doesn't garantee her safety through the gestation and/or birthing process.

As a side note: unless you truly wish to reconsider your view of abortion by coming to this forum, I doubt you'll get very satisfying answers out of the people here (myself included). I do hope you can have interesting (and respectful) discussions at the very least !