Incentives are different too. Outside of highly fundamentalist cultures, there isn't really a strong benefit to a family from pressuring someone to keep a child. In developed countries, children are a huge liability for the first ~20 years of their life. Meanwhile, with assisted suicide, there are strong incentives around cessation of ongoing medical care (costs), and obviously inheritance.
Between that and possibility of presenting some murders as assisted suicide, I think if the idea is to be implemented, it really needs to be done extra carefully.
Car kills many, doesn't stopped that from banning cars completely. Yes do it carefully, but no. Even people who live alone, doesn't have anything valuable, are not able to die with dignity. Must suffer.
And even then: We already allow families to decide to take folks off of life support.
How so? We don't have to create a system in which it is legal to shoot someone in the head and then claim they asked you to do it. Have it be a medical procedure that must be done in a hospital by government certified doctors. You can even require a psych evaluation before it becomes an option.
I can understand there being some gray area in which it isn't clear that the person has all their faculties to the point they can request it, but that shouldn't stop us from creating a system that works for all the obvious cases.