What do you think of “I just couldn’t stop myself” vs “they only don’t stop when they think they get away with it”? Especially when it’s not in terms of domestic violence, but other fights. How well can people be expected to stop themselves in a fight?
Your ability to effectively moderate your use of force scales with your training. The more training you have, the less force you need to neutralize your opponent. The less force you use, the less risk of something going horrifically wrong. Also, the better your training, the more control you maintain, which further reduces risk.
Now, it’s critical to understand that even under the best circumstances, accidents can, and do, happen. Additionally, live combat is never, “the best circumstances.”
This is almost never couched as, “I couldn’t stop,” usually, it’s more in the range of, “I didn’t mean to do that.”
It should also go without saying that if the person using that argument is the aggressor or the victim carries a huge impact on how its viewed. An aggressor who says they couldn’t stop is going to be viewed in a far more hostile light. If it’s the victim, depending on exactly what happened, this could be viewed as little more than an understandable accident. Worth mentioning that the phrasing you used leans heavily on the idea that the character was the aggressor.
I’m not 100% sure what you meant with the second argument.
“…they only don’t stop when they think they get away with it?”
Again, there’s a legitimate read, and an illegitimate one.
If you look at it as using enough force to “get away.” That’s the threshold for normal self defense. (Create an opening and escape.) As above, someone with limited training and experience can be forgiven for exceeding this by a substantial margin in the moment. The more training you have, the narrower this margin becomes.
If you’re asking about, an aggressor who only stops when they think they’ll face consequences, that’s a sadist, or worse.
There is another element to holding back, in fiction: concern that violence will, “taint,” your character, and make them unlikable. This is an understandable, if ultimately, mostly, misplaced fear. If we’re talking about your PoV character, they’re in a unique position to defend their actions to the audience. In a real way, you have far more control over how the audience views your PoV characters than any other participants in your story.
Your characters need to act in accordance with who they are as people. So, that does put some limits on what you should do with them. There’s also room for a character to be someone other than they appear, though doing this with a PoV character can be tricky, and will carry it’s own consequences.
Stories and drama thrive on consequences. A character does something, the reactions that come from other characters are dramatic. This is a good thing. Stories thrive or die based on their access to drama. This can include situations where they’ve gone too far. Dealing with the consequences for that, are a dramatic goldmine. It’s nice when everything goes to plan, but it’s interesting when the wheels come off.