Struggling parents

If a parent was struggling does it give them an excuse to take it out on their child? I know a few parents who have struggled a bit in their lives. Some of them made it up to their children and some haven’t. I tried to tell someone close to me that just because people struggle in their life doesn’t mean they should take it out on their child. A lady I know was mistreated in her childhood which she ended up having two kids and both of them were removed from her care, with those two kids she now lives with one of them and the other she doesn’t want to see or speak to, she even forgot when their birthday was. I felt as if it was completely unfair and unjust to the child she doesn’t see anymore because the mother left her and couldn’t care about leaving her meanwhile it was said the mother was abandoned as a child. A lot of people kept making excuses for the mother and saying they feel for her meanwhile to me it sound like a bunch of bullshit! The mother kept saying about how much she wanted her child except she never showed up on visits, no phone calls, letters, etc.