I've learned over time that I need to speak up for ME. I have no control over what other people do. People who are going to abuse others have no concern for how their victims respond. Therefore, if someone is behaving abusively towards me, nothing I say or do is actually going to prevent them from abusing me. They're not interested in whether or not I believe that they're harming me. They're invested in continuing to harm me. I'm never going to make them understand that what they're doing is wrong. I might be able to keep myself safe from them by making them afraid of me or making them go away, but I can't count on that. It depends on how much of a threat they perceive me to be, and how desperate they are for whatever they're trying to get from me against my will.
Speaking up is a thing I do because it's self-advocacy. It helps me maintain my humanity. It has nothing to do with impacting their behavior, really.
I have chosen to increasingly embrace my own capacity for aggression, because that suits me right now, and doing that means I have more ability to deter abusers. But that's not about the words I use.
The words are for me. To tell myself that my story of what is happening is true, and valid, and worth listening to. Regardless what they believe.