If it benefits you. For example, if there are people in a specific group that you'd like to be a part of, defending the persons honor they they are condemning will not earn you points at all. I know people like to act like you can get through life being a damn saint all the time but that is such a facade. The reason the people in power are where they are is because they made fun of the right people with the "right" people. Their status grew and they could eventually form themselves how they wanted to because they had enough power to influence how others figured out who was appropriate to make fun of and such.

It's a subtle trust mechanism between people. It determines who you are and what you're willing to partake in but with minor repercussions involved if it's discovered by someone else who may care. I mean think of this, if you participated in the #metoo movement and your case did not lead to any convictions, do you seriously think anybody will not come up to that person without any trust reservations from the start? It's public knowledge you will go public with something you perceive as wrongdoing against you. So if I accidentally offend you, now I might be concerned you may use that to damage my reputation down the line.

As a former "always follow logic and be nice christian" person, you will never get anywhere butting heads with people for the sake of righteousness. You will go the way of Thomas Moore, get your head chopped off, and the world will proceed without your input interfering again.