You generalize too much about the oppress/oppressor. Most victims of all kinds of oppression DO NOT become oppressors, but you keep taking what is exceptional and make it common. That's not how things or life work.

AND, when the formerly oppressed become oppressors, it is our human duty to kick their arses just as we did to their victimizers.
Israel is the perfect example of this: from being victims of a holocaust to now becoming the perpetrators of one. Sad.