It's nice to have and good when it happens, but many arguments boil down to matters where there are, in very real terms, winners and losers.
Not everything can be patched up procedurally, nor can people "switch up" when it's eg: a black man told to try to understand the slaver's argument.
It's good to develop some capabilities to cope with difficult and heated discussions.
They don't end in agreement, they begin with cooperation; you might not resolve the argument, or your position might prevail, or even change. As you say, there is no argument to be had in some cases, there is no reason. I'm talking about a methodology, rather than an outcome; you can still disagree.
That said, in the case of something like the slave and their master, I'd suggest that an argument is pointless in any case; what's needed is a fight (in the literal sense).
Like abortion, or wealth inequality, or police brutality, or gay rights, or race and IQ.