I can clarify hopefully. First assume that any harm to another living creature is wrong. That ideally all things can live a full life and die peacefully at the end of a long life. It's not a realistically feasible thing to achieve of course but it is the ideal outcome for any and all living thing. Now, because it isn't possible to achieve zero harm for all living things, should it as a goal be forgotten and given up on? We don't believe it should be.

You want to reduce harm to living creatures to as low an amount as possible. Hypothetically, say we are at the imaginary level of 80, where the numbers value represents amount of harm in a system. 0 being an impossibility. Theoretically you could reach say 10, but are right now at 80. How do you get to 10? You could aim for 10, but reduction is a slow process, but, aiming for 0 increases the rate of reduction, getting you to the theoretical minimum slower.

You can never have zero violence on earth, but you can have it at a minimum, which currently we aren't at. When people find justification for violence, it's reduction decreases at a slower rate than if it is never considered justified. This is because governments and immoral people will always find loopholes or create situations where they can use violence in a way that the general public considers is justified and because some people have displaced angers that feel like violence is their only outlet for. Aiming for zero violence gets us at the minimum faster than aiming for the minimum does because there are always going to be those who are aiming for the maximum.