I support abortions in most situations. The ones I don't care for are when the mother consistently gets abortions as a way of preventing birth due to failure of using things such as condoms, birth pill, etc... . I still support it here but I find it to be irresponsible and almost an abuse of abortion clinics.
In the case of the
OP, there's several things to consider first, such as was the sex consensual, did the father provide enough monetary and "parenting material" to help your mother, was the financial situation between your mother and father generally poor, was your mother facing immense stress that having a baby pushed her over the edge to make her think she couldn't handle all of it so she needed to reduce some stress and many other factors. What's clear though is since she did not have an abortion with you, one of these factor(s) or another factor(s) were different, and so the situations when she had the abortion versus when she had you were different. Something must have led her to believe that whatever the problem(s) were before, they were reduced or even eliminated when she had you, allowing her to be a more fit mother.
Yelling at her is simply childish because if you want answers, talk to her about it and have her explain the differences in the situations. Her having sex with your father could be anything from her also being drunk, him being violent, the two being consensual, etc... .