Bangladesh this month executed Muhammad Kamaruzzaman, a senior leader of the Islamist Jamaat-e-Islami party, for war crimes committed during the country’s independence struggle more than four decades ago. Prosecutors accused Kamaruzzaman of involvement in widespread rape, torture and murder as he and his cohorts fought a losing battle to ensure that Bangladesh remained part of Pakistan.

Instead of applauding Bangladesh’s efforts to close a traumatic chapter of its past, Western governments have been lukewarm to hostile. While...