You're shifting the argument, moving the goalposts. You said suffering could be useful if it helped develop compassion. No one said compassion wasn't a valid trait, but that the method of developing compassion ALSO created incompassion, so the method was clearly faulty (also it killed 250,000 people, so there's that).
Now you are judging the method of developing compassion, which is perfectly fine and accetable, BUT that is a different issue.
If the method used to create/develop compassion is not 100%, then why is that? and what method would guarantee compassion to be developed 100% without infringing on a persons right to NOT be compassionate?