Another possible scenario could be that shortly after her son was born, Rita "left" Zedd with the baby to pursue obtaining the power we all saw in MF. As time continues, the son questions his past, and what his mom was like. Zedd tells him the whole story (including his evil past), alongside why Rita left him. The son then starts to question the "good power" that his mom had left to pursue because it resulted in him not knowing a mother, and his dad being left alone. The son proceeds to search for his mom. On his journey, he learns of the "two sides" to power, and chooses to believe evil is superior. He then comes across the new rangers (OO), and has intentions of getting revenge because he believes the "good" is responsible for him not knowing his mother.