The reason he overpowers her is because she's a thing, not a person. Deckard doesn't kill replicants, he retires them.
The guilt, along with his confrontation with the other Nexuses and the (ambiguous) realization he's the one doing the dangerous work because he too is not a person, is what changes him.
Totally agreed that societal mores change over time and you can retroactively realize that something wasn't OK.