They were banned for being inhumane, not not militarily useful. The international community doesn't like the idea of military actors running around with weapons

They were banned for being inhumane, not not militarily useful. The international community doesn't like the idea of military actors running around with weapons that permanently cripple but don't kill; landmines are probably a better example of a banned weapon than blinding lasers. They're highly effective military weapons, but frequently leave victims alive and in need of critical medical care, and then support for the rest of their lives; incredibly terrifying and demoralizing from a psychological perspective. Countries that care about their soldiers don't want their soldiers to worry about that. The blinding lasers are similar: how many volunteers could the US get if there was a high risk of "merely" being permanently blinded, and then discharged?