It's sad that these scammers are victims themselves, but measures that reduce the extent to which these victims can victimize other people are a clear net good for society. You won't save a trafficked scammer by hanging up early so he can move on to easier marks, but you can prevent him from using the next hour to make a new victim out of somebody else.

Or to put this in other terms; you're a Ukrainian machine gunner. In the distance you see Russian soldiers. You know that many of them are from the Russian gulags, unjustly imprisoned in an oppressive autocracy, quite likely for a crime they didn't commit, and now forced to invade a foreign country. You pull the trigger and mow those victims down, because if you don't those victims will make victims out of your friends, family, and fellow countrymen.