No, "men as a class" is an abstraction, something that you could, for example, make a statistical statement about.
You can't blame men as a class for a specific action. That's not what blame is. In fact I think that blame as such is not a very useful emotion, it's a way of discharging a certain amount of emotional pain, but it's not really the best way because it is so prone to the kinds of falsities you are trying to justify here - you have to find someone to pin it on, or you have to shift it from places that cause more pain. An abstract entity like men as a class seems ideal, as it doesn't seem to impact anyone real, but it stops you from seeing what's really happened and it also could well end up compromising your ability to have good relationships with individual, real men.
I think what you are really trying to get at with your mum is thinking about the extent to which she is really culpable for her actions. Often when any of us do bad things, we have only limited culpability - things really do get in the way of people being their best selves and making the best choices. Lack of understanding, lack of good role models, emotional distress, some sort of compromised self-control or decision making, fear, illness, addiction. You could go on and on.
It sounds like your mom had a hard time, and all kinds of barriers to doing what she ought to have, and maybe should have. It's even possible that at by certain point in her life, addiction meant she had no real ability to make choices - drugs can sometimes have that effect, destroying our capacity for choice. In most cases though, people do bear some responsibility for choices they made along the line, most of us have a fair amount of responsibility most of the time. Maybe only rarely do we make a perfectly informed, willed choice to do evil because we want to and decide to in free way.
Ultimately, we can't know how much at fault others are, we may guess, but that's what it is. Often we don't even know with regard to our own self. If you can let go of the need to figure it out, it's very healing. You may or may not be able to have a relationship with the person at that point, if you can, that's great, sometimes there has been too much damage.