Pointing out that "both sides" do something doesn't mean that thing is acceptable or moral and is often just a deflection.

It's fine to point out that "both sides" do something if it's in response to the claim that only one side is guilty of something, but rarely is that the case from what I've observed nor is it the most important point. Generally it is a way to stop talking about whatever the "thing" is. If A and B have both done X, that says nothing about whether X is right or wrong. That's why it's often more useful to discuss the behaviors and issues themselves (the "X") rather than the people who engage in them (the "A" and "B"). Pointing out hypocrisy does not close the discussion of the issue at hand. This seems especially relevant in political discussion and why political discussion often goes nowhere.