Ok, op, I work in social work, and a big part of my job is training new Social Workers on placement.
Initially there's nothing wrong with your initial question. You are aware of a judgement you are making and asking the right question- why do people behave this way. If I were your practice educator, I would tell you that you need to do a huge amount of reading to understand the answer. Look at theories of change to understand why some people can achieve it, and some don't. Look at theories of resilience to understand why some people don't seem to have the resources to cope. Look at anti discriminatory theory to understand the impact oppression has on the human mind. As a Social Worker you can't throw your hands up and say "Well they just don't want to change!" You have to work out why, so that you can help them to sort it. For some people, they are so damaged that you have to go right down to the roots.
As a Social Worker, you need to be able to reflect. On your own experiences, on your own reactions, put them under the microscope and work out where they come from. You need to be able to understand and defend the judgements you make from a professional position, not a personal one.
What I am seeing however on this thread is an attitude of you being convinced that you are right and not being prepared to actually move. You are defensive, not reflective. That is the most dangerous trait there is in a potential Social Worker, and if by the end of placement, you hadn't managed to address that, you would fail the placement.
I'm also concerned about the values you are defending here. There appears to be a cut of point for your sympathy. Children are to be protected, but adults just have to get on with it. Those adults were children once, and many had the most horrific time, which has left them damaged. At what age are we meant to stop caring about that? We can make a professional judgement that they are not capable of looking after a child, but to have no empathy for the adult is unacceptable. Also, to suggest that because you can't forgive something painful in your own personal life, a whole catagory of people should die? And their children should mourn them, their parents, their siblings should all suffer the ultimate loss. These values are incompatible with Social Work, and if you can't reflect on them, then it's the wrong career for you. You would burn out very quickly, and do a huge amount of damage on the way.