You've chosen to charge straight into the minefield there: that's possibly the most controversial thing you could say, it has all sorts of implications in all sorts of contexts as diverse as abortion and Palestine.
This is fair. You can't really have a good debate with anyone if you don't agree on first principles. It think that's part of the problem with the worlds polarization these days.
We have this fundamental disconnect between 'the greatest good for the most people' on one side and 'the greatest good for MY people' on the other. It's literally two different answer to the question of life having value. IE - "They all have the same value." vs "Some are more valuable than others."
When you have disagreements that fundamental you will never find common ground. The zero-sum view of the universe is fundamentally incompatible with the other view.
The only way to stop it from becoming a thought terminating cliche when it comes up (in it's many forms) is to explicitly call it out as what it is - A fundamental an insolvable disagreement that can only be met with some level of compromise.
Note well that this may not work to persuade them. But you can at least have the conversation.
It is noble to try. I suspect that you will always fail, unless the other person is uncommonly reasonable. Those views of life are the result of having vastly different experiences and backgrounds, and aren't something that typically changes after reaching adulthood.