I agree with what you say, if it were an isolated event. Just one person killed by Balefire is no big deal. It won't unravel the Pattern. Every single place where it's been used can be rationalised. Kill a few Forsaken. Kill Darkhounds to save people from dying. Undo deaths caused by people. And so forth. The more Balefire that is used, the greater the risk to the pattern. That's why it's not acceptable to Balefire Mesaana. Where do you stop? Where do you draw the line? If you don't, at some point, it'll ruin wreck the Pattern beyond repair. That's why Aes Sedai have outlawed it.